Basic Guide to the Meta: 4 top that are good teamfighters, 1 bot that either can farm safely or is strong 1v1. Avoid rotating/ganking bot unless you already have at least three points captured. Send an effective duelist or roamer to the center of the map for the Storm's Surge buff when it refreshes.
Basic Guide to game strats: Run at least one person with {{summoner:17}} (usually your solo laner) since it sets up dives and stalls ganks really well. It even blocks someone who is in the middle of trying to capture your turret!
Pushing past mid is scarcely necessary. It is usually a more viable strategy to capture the three points closest to your spawn, and then have 1 or 2 stay to defend while the others back to base.
Occasionally, a Secondary Objective indicator will appear and two turrets will be marked with either crossed swords or a shield. If your team captures the swords point, you get increased damage for one minute. If the enemy team gets your shield, they get the damage buff instead.
Objectives>Kills. Avoid chasing the enemy when you could be capturing a point. Conversely, it is usually worth it to sacrifice yourself if it prevents the enemy team from neutralizing/capturing your turret.
You get a free revive at levels 1, 9, and 14 that you activate by using your trinket. Avoid using your charges before the 7:00 mark. It is a priority to use a charge if you are approaching level 14 and have 2 charges or if someone is capturing a point just outside of your base.
Recall timers are halved, so don't be afraid to abuse that by backing often to stay healed up.
If you are even in champions while attempting to take a point (4v4, for example), try pushing the minion wave and sieging the point. Enemy turrets WILL NOT FIRE while a champion is attempting to capture, so use that to keep your minions sieging as hard as possible.
If you have at least one more champion then the enemy (2v1, for example) have the champion that deals the least damage attempt to capture while the other players dive the enemy. As said, the turret cannot help if someone is capturing it.
If enemies are attempting to capture a neutralized turret, you can stop all of their captures simultaneously without even damaging them. All you have to do is right click the turret and wait for your capture animation to complete, and all of you will return to idle.
Basic Guide to Champion Selection: There is currently no champion.gg for Dominion, so it's mostly conjecture as to who is truly the strongest. In my experience though, there are factors that make a champion especially strong in this game mode, and I will list them from most to least impactful, along with examples.
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Strong teamfighters

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Effective roamers

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Good zone control/point defense

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Late game assassins

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Peelers (especially those with self peel) and Kiters

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"Mana Gated" champions

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Warding/Scouting ability

Almost all champions combine more than one of these factors, for example,
is an effective roamer with self peel and a scouting ability. Experiment with a few of your favorites and you will quickly settle on what works for you. Here are some factors that make a champion unfavorable.
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Scales with farm

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Unable to function alone

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Cripplingly immobile/need Peel

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Falls off late

I'm not putting down these picks as unusable, I'm just warning you that if you pick a champion with one of these traits, you must be prepared to play around it. For example, I've had outrageous KDAs playing Kog'Maw because my team had 2 supports and I refused to stray 3 Teemos away from them.