Runes...I like MPEN, Armor, Move Speed, and then either magic resist or mana regen. I think my masteries are 0/21/9. I always get ghost.
I like top because I feel that he requires too much farm to play support.
I never expect to get hero kills early on.
I push aggressively when I can. By push, I don't mean hit the turret, I mean walk past their turret poisoning all the incoming enemy minions and then hitting the turret.
I'm not that good, so I won't try to give advice as to how to fight enemy heroes. Generally fling enemies that are attacking your ADC or AP away from them, or selectively fling (Amumu is generally a bad one to throw into the middle of your team) out of position enemy heroes into your team. In team fights, I seem to generally dive bomb the enemy ADC which disrupts them.
I think Singed is great bait and a great split pusher. If you get your team on board, split push, have your team wait for them to chase, after they've chased a bit through your poison, your team can pounce on enemies at 3/4 health.
Items: Mana crystal, health potions
Boots 3 (or Merc or Tabi)
Then it gets more situational. I love to get a Rylais, but sometimes Thornmail or Banshee's Veil is a higher priority. I've never been crazy about Sunfire on Singed.