Well, you can't really change the hardware, so the short version is not much.
The long version is this: you might see some marginal improvements by being a little more mindful. Make sure your device is up to date, in terms of software. Try to remove any unused or unnecessary apps, particularly ones that like to run in the background. Close apps after you're done using them, instead of letting them sit in the background. A factory reset is also a nice way to start fresh, if you don't mind losing things. Rooting it might also be something to consider, as it would allow you to remove a lot of the bloatware that comes pre-installed.
If you mean its performance IN apps (games and stuff), that's hardware related and really not something you can change. Turn down graphical settings where you can.