Hi Brandon, welcome to the forums! One of the quickest and easiest ways to improve battery life is to perform a factory reset, especially if this is a new device for you and you don't have lots of data already saved on it. In any case, back up whatever you do have so you can put it back on after the reset.
You should find Factory Reset in the Settings menu or you can hold the ''volume down'' button when you power it on. Another thing you can do is fully discharge the battery and then fully charge it again. Depending on the battery type this will sometimes ''reset'' the battery capacity to something closer to what it should be.
You can install a battery/power management app (there's a lot to choose from in the Play Store) and possibly a task killer app too to stop your tablet from working too much when it doesn't need to. You might also have battery conservation options (eg dimmer screen, etc) in your battery settings on the tablet.
As for custom ROMs, that's a whole other story! Maybe try these steps first to see how fast it gets and whether the battery life is ok, then the options are to get root access and flash your own ROMs, w hich we can get o later. Have a read of this introduction
As for the battery life however, if the above tricks don't help, you'll just have to buy a new battery (if it is replaceable). Custom ROMs do give you more control over how apps are used and that would give you better control over the battery life. All the best!