(SUPPORT) Swain is a very strong early champion. His E and Q combo are extremely valuable, but you need a reliable adc to dish out some damage too. The fact that he's very usefull in case of invades is also very important as it can give your team an early edge that sometimes is all that is needed to pile up and snowball. At the beginning, giving yourself a bit of mana, damage and tankiness is something that will set up the base of your game. Dont hesitate to help the mid lane a bit whenever the enemy mid is pushing hard.

(TOP) Swain needs some space and manoeuver to make some good early plays top lane. Since your damage is based on your abilities, you'll have a hard time facing champions such as Jax or Darius at first. Ask your jungler to come and help whenever he's top side, and make sure you're not pushing too far at any time during laning phase. Freeze the lane and make sure you stay near your tower. At the end of the game, you'll be an absolute monster, dont even worry about it. Focus on farming.

(SUPPORT) Swain can seem to fall off a bit in the mid game if your start wasnt very good. The idea is to never be caught alone and to rack up some assists in team fights. You have the chance to still dish out a lot of cc regardless of if your game is strong or not. If you are having a positive game, make sure you help your jungler get some objectives and dont be afraid to push with your teamates and put some pressure.
You wanna finish your Zonya asap in order to pull out some combos, bait your opponents in unexpected teamfights and give them opportunities.
Your 3rd item marks the end of the midgame, whether you went with Demonic Embrace, Banshee's Veil or any other offensive item. Afterwards, you want to build pure offense.

(TOP) Mid game is when a top Swain starts roaming hard. Not in the enemy jungle or even necessarly in yours, but to help in particular situations like a fight mid, a herald, or even a dragon. Dont forget that you can help your team at a distance with your W and that it can save the life of a fleeing ally or secure a kill.

Without forgetting about your top, Swain is a bit dependant of the rest of the team midgame, unless you've had an amazing start up top. Dont set out alone, make sure you're surrounded by other ally players.

(SUPPORT AND TOP) This is when Swain shines the most. Late games should be your strong suit considering the scaling that you have when you build up well. At some point you should be able to dish out some heavy damage and heal quite well in an ult combo. Your role is to clear out the enemy adc or any other damage built characters that are trying to carry. Never do it alone, priorise team fights as much as you can, since your ult is an area damage that will put your team to an advantage.

Your three basic abilities reach their full damage potential when they're cast in a particular order.

Your E is your initiator for a classic full combo: you immobilize the enemy, but dont pull him yet. Cast your W between the place where he is immobilized and where he will land when you will pull. That way, if he chooses to fight, your W lands. If he tries to run away, you still get him as well.
When E has landed and W is cast, you pull. Make sure to make this quick before you loose the capacity to pull or that the W ends. When the enemy is pulled and receives the damage from the W, cast your Q. You can hardly miss since the enemy is slowed from the W. Since it was impaired, your Q will deal more damage.

The other full combo option is when the enemy is out of your E's reach. You can cast W to slow him down, reach and use E, then pull and cast Q. This will provide a lesser oportunity to finish the kill but its very usefull if you're trying to finish off a low health champion. If you're low on HP as well, ult before you pull in your E.