Passive: Empowered Bulwark - Increases Singed's health by .25 for each mana point he has.
It's nice to have, however it doesn't make or break singed so don't mana stack or anything. You aren't ryze!

Q: Poison Trail - Toggle: Singed lays a poisonous trail which deals 22 / 34 / 46 / 58 / 70 (+30% of ability power) magic damage per second.
What enemies hate you for: a giant cloud of poison in their face. Really all there is to this ability is to make sure you keep that purple cloud in the enemy's face as much as possible. This means for the most part you are going to want to run in front of them. The perfect time to let them have it is right after you Fling. This is also a very nice ability for farming minions, however you want to be careful to not do it too much early game as he does have mana troubles early. And, if you want to be cocky and think you can stay alive, you can run close enough to the enemy while they are chasing you and lol as they get poisoned to death.

W: Mega Adhesive - Singed throws a vial of mega adhesive on the ground causing all enemies who touch it to be slowed by 35 / 45 / 55 / 65 / 75% for 5 seconds.
Don't quote me on this, but I think at level 5 this may be the strongest slow in the game. Regardless it's great and just one level of it compliments singed so much. You will notice the delay on the adhesive when throwing it so aim ahead accordingly. There are 3 major uses for the slow.
a) To slow the enemy so you can catch them and Fling them.
b) To slow the enemy who has already been flinged so you can continue to give them a good drink, as well as allow your teammates to hit them.
c) To save team mates/yourself from chasing enemies

E: Fling - Singed flings an enemy over his shoulder, dealing 100 / 150 / 200 / 250 / 300 (+100% of ability power) magic damage and slowing the enemy when they land.
OK, I lied. THIS is what enemies hate you for. Fling is the reason singed is a viable tank, and you are going to need to learn to use it.
First off, and this mainly applies early, you want to disguise your Fling. Don't just E+click the enemy and hope you catch them, you will get kited and loled at. No, do something such as attacking autoattacking the minions or baiting their melee champion to autoattack you as you run away (then you turn and fling them).
Secondly, make sure who you fling is appropriate. Don't fling their 4000 hp mundo with a sunfire cape. Try to get their melee carry. If you can't or they have none, then you can venture farther back and get a ranged champion. You control the teamfight. Make sure who you fling is who you want your team to focus down and kill. Taking tanks is ok, however you'd better be sure that they are going to die FAST or it's a mistake.
Finally, you want to protect! This is pretty obvious, but you are the tank and as the tank you want to make sure your carries don't die. If they are getting attacked or chased, make sure you fling the assailant away.

Ultimate: Insanity Potion - Singed drinks a potent brew of chemicals, granting him 35 / 50 / 65 enhanced damage, attack speed %, ability power, armor, movement speed, and regeneration per 5 for 25 seconds.
When the time is right, take a sip of your insanity potion and let 'er rip. Add ghost to the mix(no pun intended) and you are going scary fast. Use it for ganking, escaping, and initiating for maximum effect, however if it is off cooldown and it is you alone at an enemies tower go ahead and pop it, it's actually very good for tower killing.