Sure, I can throw a few tips. Mind I'm no plat player or Singed main.
Firstly, I feel Singed is pretty dependent on high early game MS, so get some MS quints and masteries. You wanna get those flings off. Others prefer AP or more tank, but I dunno, I feel MS is just better.
Because Singed has no real poke, whether you play aggressive or passive really depends on match up. More or less, unless the enemy has never fought a Singed before, you pretty much should expect to go 0 kills in lane. When you play aggressive it's to get them out of lane so you can cs in peace. I don't really recommend the proxy farm thing a lot of players do unless you're super confident you can get out alive, so ward up and keep an eye on the other lanes. Ever since his Ult had its Tenacity removed proxy farming has been way too risky for my tastes.
Match Ups are pretty straight forward. Do they have on demand shields? No kills for you. Do they have DOTs, such as Cass? Play super passive, they have more kill potential than you. Typically I like fighting tanky people, Shyvana, Renekton, Garen, etc. I wouldn't say the lanes are auto-won but you can pretty much ignore them for 2 or 3 waves of cs, go B, and race the minions back to lane if teleport is down. If they're ranged, well, it's gonna be a tough lane but all you gotta do is farm. Ask for ganks and just go even in lane. Always ward. You don't want to be farming at turret because you'll miss a lot of creeps, and Singed can't really freeze the lane so you'll be over extending often.
If you really want to get some kills, try to sneak a few poisons on them by quick-toggling your Q while csing, then all in once they're health is lowered to ~70%. They can't out run a Singed, Ghost, fling into poison, run circles around them and spam laugh (don't forget to AA!), slow them after the fling, fling again if they're not dead yet. Bring ignite if you want kill potential, bring Teleport for late game hyper-tanking. But you NEED Ghost. Don't care what Mobafire says.
Build wise, few things you can do but the tried and true build for me is:
Rush Rod of Ages, next item should either be Frozen Heart or Spirit Visage (your ult is super boosted by it!), then get Liandries and you're done with damage, buy the other item (FH or SV), then just go full tank/HP. Randuins, Banshee's, Rylai's is nice, Warmogs probably works well though I hardly bother. Boots are match up dependant, but I like Swiftness for the slow reduction. But if they have 50 stuns it's obvious which boots you should go for.
Sorry for the wall of text, heh.