You really need 2 things to get a significant increase in performance - more RAM and a faster CPU. And you can't do that.
Small improvements? Find a kernel you can change speed on and run it a little faster. Decide where you want the improvements. Some launchers are faster than others, but if you spend all your time playing solitaire you're not going to care how fast the launcher is.
One thing that doesn't improve performance is app "killers". Android does a great job of managing which apps should stay in memory, which should be suspended and which should be dumped. If you start killing apps, you'll usually slow things down. The app you think you don't want running may have code that the one you want running has to call. So by killing the "unwanted" app, you make the phone waste time reloading it the next time it's called.