Guide to Modding your G2x
Installing ClockWorkMod Recovery(Included in the above, but posted anyway)-Includes instructions on how to flash back to stock recovery, important if you want to return your phone!
2.3.3 Gingerbread Stock Rom-Needed if you want to return your phone in factory condition, but forgot to use CWM recovery to back up your factory ROM, the one that came with your phone
The third link above has the instructions on how to root it.
1. Try undervolting and overclocking your phone. I've used SetCPU (free on xda forums, google "setcpu xda" or something like that, should come up) to do that. You can extend battery life that way.
2. After you first install ClockWorkMod recovery, go into recovery and backup your phone. You want to keep that backup so you can restore to it the day you decide to return your phone.
3. Consider getting an extended battery on eBay. I got one for $8.99 on fleabay with a replacement back door that doesn't look or feel to bad. The only downside is my phone is almost twice as thick as before, but not a problem for me. Now my battery lasts a long time.
4. Juice Defender is always helpful with saving even more battery life.
The G2x is probably one of the most underrated phones of 2011. Its CPU/GPU performance puts it on par with the Galaxy S2 and makes it even superior to the venerable Galaxy Nexus.
My Browsermark Benchmarks