I'll keep this post short since it's almost 2 AM for me here.
A very interesting way to win a game I've found to be playing something nobody in your ELO knows how to beat. For instance, in silver ELO mid Kha'Zix with fort pot start is guaranteed to get a level 2-3 first blood, that is, unless the mid/jungler have any idea of what you are going to do, in which case they don't belong in silver anyway IMO because people that belong in silver don't usually have high micro skills and the silver junglers almost never gank pre-4.
Something even cooler is playing Fiddle support. Yea, you heard me. I beat a Thresh Cait lane with my ADC being MF the other day. Here comes the good part:our Jax top went exhaust/ignite(yea, no flash) and fed their Riven hard, then she started roaming to try and kill us in teamfights. We beat them 4v5 because other than her, nobody else was fed and I kept her away with my 3 second fear and my 1 second silence, giving her very little time to do anything in teamfights. Lategame we won because their Jarvan was being a typical low-ELO jungler and kept ulting a Fiddle-MF-Kennen teamcomp, effectively murdering his team. Yes, I was flamed at in champ select, however I picked Fiddle knowing I could stop the conflict that already started between my ADC and our toplane in champ select because he wanted to go top instead through playing support and getting him fed while protecting him in teamfights.
Alright, I guess I'm going too long. To keep it short and simple, play something out of the ordinary/hard to beat. What I've found so far is this:Zed and Kha'Zix are Silver mid lane kings, Fiddle dominates all the supports,(except Leona I guess, have yet to try that match-up, I figure she would be hard because no matter what, if she really wants she WILL engage), Darius will dunk all day long, while Renekton beats everything Darius can't. I've yet to find a dominant jungler and AD Carry, at least one that I'm confident enough I can pubstomp with(although Tristana and Hecarim seem to be working nicely for me lately).
Oh and one more thing, I couldn't help but notice you think Plat games are better. I've played a premade with a Diamond player and got pitted against 2 Diamonds and a Platinum, I beat the Diamond player in lane(yea, me, a Silver 4) and then we won the game. Needless to say, it was close because I won the lane, but didn't stomp, while every other lane went a bit even. The game, however, was amazing. It had that special sense of thrill, the amazing prolonged teamfights that you never see in silver(you know, the AD carry never tries to dive like an assassin or a tank, everybody actually knows what they have to do) and the 5-men-together-at-all-time thing made me feel like I'm in a very special place. That's the reason I want to climb myself. I want that sort of gameplay again. I want to feel like I'm having a great time, not like I'm just rolling over somebody, like somebody is rolling over me or like I'm babysitting some 5 year old kids. I want to be on even grounds with everybody and everybody, including me, having a cool, laid back attitude enjoying a nice game of LoL on a nice afternoon.
Sorry for the long post, got carried away I guess.