Team Work and Strategies.
Knowing the roles is just the mere beginning of everything. There are lots of strategies to consider and tips to be known.
First of all let's talk about Team Composition.
-> 1 capturer
-> 3 takers
-> 1 defender
-> 1 disrupter.
Wtf 6? It is obvious that many champions can do well in different roles. Many disrupters (-> that kills capturers) are excellent takers (like Lux or Ezreal). Many defenders are excellent disrupters (like Karthus), etc.
One has to be always on the run getting your enemies nervous capturing their CP, the takers are in constant fight over enemies Capture Points and there is always someone trying to secure one of yours, being poked by an enemy taker. But this does not always happen, Dominion is HIGHLY situational.
Early Game Strategies.
I will assume that you know that what comes next are just mere ideas. They aren't they way Dominion is meant to be played, that's obvious, but they have proved themselves useful. Almost anything could happen at the beginning of a match, but some player behaviour is predictable and you can do something about that if you are smart.
The Windmill: also known as "Top", is a very conflictive capture point. It is the most distant CP from the base, being at same distance from both team's spawning place. At the beginning, the team that gets the Windmill usually is the one that deals the initial damage to the other team. So, secure the Windmill.
One idea is this: 3 have to go to the windmill. 2 have to be kinda tanky, melee if they can. The third has to be a caster with CC. One of these three should be your capturer, the first one to reach the place and start the capture. The caster Mustn't capture, it has to prevent harassment so your allies that are capturing can do it without problems. Your caster has to use its CC and whatever it can to avoid getting the ones that are capturing from attacked. If this fails, the team that disrupted (arrived later) is on a slight advantage because they attacked you to disrupt, so you have a bit of HP less.
Now starts the Windmill Fight, quite an event. It is ideal to win it to start good, so the best choice is to have one more champion than them. The two that didn't go to the windmill should go there asap if they see many enemy icons in the minimap. Now a common strategy is the 4-0-1, as people start to see top's importance. Remember that can Never cover all of the things you want at Dominion, so that "0" in the enemy strategy should be used for your advantage.
Quid pro Quo: it is common to see everyone focusing on the Wmill, and it's a nice opportunity for your capturer to start its job. Imagine you are the left ones, so you have the Quarry and the Refinery close to you, and the Drill at right top, and the Boneyard at right bot. When everyone is on the Windmill, the quid pro quo idea is to send someone to capture their side-top (right top, or left top; Drill or Refinery). This is highly annoying, usually nobody defends these spots at the beginning and the ones that are fightning on the Windmill don't know if keep fightning or go to their being-taken CP.
Mid-Game Strategies:
Roles and rules in Teamfights: Capturers are supports or tanks, actually the only tank capturer is Rammus, the other ones are supports or stealth champs. Takers are carries and casters, Defenders are tanks and some are casters, Disrupters are dps melees or full AP casters. The important part is that all this isn't even noticed when you are fightning, in Dominion people just... fight.
Well... -you- have to be smarter. Remember how you used to think in the Classic mode. The Golden Rule: if they are more than you, retreat and ping. I have seen so many teammates fightning 2v3, 2v4, 2v5 as if there was only one enemy and it is quite hard to understand why they do it. Everyone is just driven by the recklessness and fast paced stuff, they don't seem to remember the important and basic principles.
PING! two roles ping: capturers and defenders. Takers (the ones that do most damage) must Whenever possible go to the pinged places, prioritizing Defenders. Defenders are just buying some time, waiting for their teammates to gank the enemies. Capturers should be able to escape just fine, but if they are being chased all over the inside roads of the Crystal Scar, someone should aid them asap.
The quests: perfect scenario to prove your skills. Your defender must stay at the Cp that has to be defended (marked with a shield on the minimap). Your capturer must go to a CP that isn't the quest's one, to distract your enemies. And your takers must do one of these: A) help the defender if the enemy is rushing into their quest's CP; 
gank the ones that go after your capturer or C) take the quest CP if it isn't being heavily defended.
Quests may drastically change the course of everything. They put everyone on the move, make defenders change places and capturers to get mad about capturing that particular CP and rushing recklessly there. Just... focus on it! If you accomplish it, it is a cool
-20
to your enemies' nexus (it's like killing 10 enemy champions). When a quest is on, try to avoid dying and going b, use the healing spots.
Dominion Baiting 101: by mid game your enemies should already clearly know who your bothersome capturer is and have someone always chasing after it. If it is a Nocturne, well, best of lucks. But if it isn't, two takers (good at damaging) should be in a bush near the CP your capturer has just been trying to capture. Common capturers would flee, in this case you will stay, looking weak and delicious. Normaly two is the maximum number that goes after a bothersome capturer, so you should outnumber them. Besides you have the surprise factor and a good support (your capt.).
Relic Baiting: the Ring is obviously the big circle where the CPs are. That area and the relic's area are always visible spots. Seeing someone in the mid of your minimap, knowing he is getting a strong self-regenerating shield (the relic) makes most teams want to kill that champion as fast as possible. When someone is going for the Relic, it has to ping or say it on the chat. The relic is for takers, or in some cases for the defender; but takers tend to need it more. Always, always someone has to be near your relic taker to protect and help, it is a very frequented spot. If you are more organized, plan the baiting and simulate lag or indecision, meaning: if there is some allied champ near the bush waiting to gank and you are taking the relic, try to be visible in the minimap as long as possible. Go to one side, then to another, stay quiet, then to another, and someone on the enemy team should have pinged you already and two might be going to get you. Capturer's that are always moving should be close to help and support.
CP harassment: strategy mainly used by capturers. Not everything is capturing, it is about neutralizing too. Do not stay for the capture if you know they are going to get to you quite soon. If you don't see at least three enemy faces on the minimap, neutralize and run to neutralize another thing. Sometime, someone will have to go and recapture that point, while you are neutralizing another one. When you are being hardcorely chased, ping yourself (use "G" on your keyboard) and ask for help. Remember capturer, you are important. Kinda. (/joking).
Late-game Strategies:
The Hare: (capture, run, capture, run) if your nexus has more hp than your enemies, then start a capturing frenzy. It's as if everyone is a capturer, go for those CP that are all alone (better if you go in groups) and take them, if someone comes, leave to another one. Sometimes this enters into a quite fun game mode: the enemy team starts to do the same! "If they take ours, we'll take theirs!" but they are at hp disadvantage, so as long as they follow this capturing - countercapturing game, they'll be losing life over time. This is quite risky, because if you lose a team fight doing this, you may have lost the game. Nevertheless, worked for my teams 4 times already.
The Turtle: (defend with all your skills when you have majority) this strategy gives full importance to your defender. You should have three CPs and try to keep them for as long as possible. Sooner or later your enemies should do one of this two options: A) Rush all five to get that CP they so desperately want or Rush to the less defended one. Be aware of their movements, go there, and kill them if you can. Remember that they are rushing to Your CP, so it's your personal slow short-ranged lovely turret that gives you a slight advantage. Summarizing: defend for as long as you can! Takers should consider using Garrison to heal their CPs. Don't forget to tell your disrupters to be constantly using their global skills to stop anything from being taken. (Btw, Luxes rock at this, such a low CD, such a strong and long ranged ult. If you want, check out my Dominion Lux build here).
The Swarm: (rushing a CP in a group of 4 or 5, then another one, and disperse) risk incarnated. It is used against Turtling and it usually goes out kinda well. All your team has to move to the same CP, one that has only one innocent defender on it. It is ideal if that CP has another enemy CP close. You shouldn't move through the ring, and shouldn't go through the relic's, in order not to be seen. Kill the defender as fast as possible, fast capture the CP and all five rush to the closest one and capture it too. By this time, you should be seriously counter-captured, disperse and leave one defender on the new CP that you got. Do this only if you have some good team composition and feel you can succeed if a 4v5 or 5v5 fight shows up, which tends to be the answer to this kind of behaviour. Yet, the swarm is cool because teams are usually dispersed all over the Crystal Scar. Don't do it often though, they can esaily take the CPs you left unprotected, unlesssss... you have a good disrupter ( Karthus, Gangplank, Ezreal, Ashe) to stop them. Be wise, b if you have low hp, or b if you think you'll get faster by b-ing.
The Ants: at late game you should all have lvl 15>, meaning you are quite strong. Guess who isn't? The minions. It shouldn't take you lots of time, but whenever you see en enemy minion, kill them. You get gold, and by the time your enemy realizes, their CP will be shining in red with no enemy champ face next to it. Bothers a LOT. Usually minions are enough to neutralize. Common teams defensive instincts activate when they see a big face next to their CP on the minimap, if you try to kill minions from the jungle/inside roads, would be better. But do it fast and leave. Do this only if you are at advantage and have majority.
gank the ones that go after your capturer or C) take the quest CP if it isn't being heavily defended.
