This is my Swain guide on how to do tons of damage. Your enemies will never know what hit them.

For runes, we need attack speed. Get a bunch of each color, because 9 isn't enough. Now we attack really fast.

For masteries, we want to do tons of damage, so grab everything that makes us do more damage in offense.

For summoner spells, use Eye of the tiger, and Jesus man.

For our skill sequence, we need to grab the birds first. Then get the green ball, because it helps us do tons of damage, and then put one point into the flying bird, and the ground claw. Now max out your birds, and put the rest of your points into the green ball, because it will help us deal even more tons of damage.

You should never go into battle without some defense, so grab the shield. Then when you have the gold, get some shoes, because you should never run around barefoot.

Our first big item, is Trinity force. It does tons of damage, so there's no reason not to get it.
From there, grab a staff, hat, and sword.

Now that you are fully equipped, get out there and do some damage!