The more you ask your Android to do, the harder it has to work, and that's going to have a detrimental effect on your battery life and/or speed, so once the novelty has worn off, take a look through your installed apps and decide if you really need all of them? What about the number of home screens you've got, and any widgets you have running? I'm not suggesting you get rid of them all, they're a great feature of Android devices, but just take a quick look at the ones you've got running and think about how much you actually use them. What about screen brightness, if you're not using auto-brightness, maybe you could turn it down a bit, and save some vital battery when you have the screen on?
If you have any apps that connect to the Internet (weather apps, Twitter, Facebook, etc), they usually have an option for how often they refresh their data. Do you really need the weather forecast to update every 30 minutes? No, then change it to something less frequent.
Although Android is designed to keep tasks in memory, you do sometimes find that you have some apps or services running that don't need to be and it's worth keeping an eye on them in Settings > Applications > Running Services. Make sure you kill anything that shouldn't be running. Make sure it shouldn't be running though, because if you kill the wrong thing, you might be doing more harm than good.
If you've got root access on your Android, and it came with some bloatware (apps installed by the manufacturer or carrier) that you don't need, then you can delete them from your Android's system/app folder, although you might be better off using a backup app to backup and uninstall them, in case you decide you do want them in the future.