After a full charge, use the phone for few hours and then goto
Settings-->About Phone--->Battery Use
Check what is consuming the battery most.
There are certain system apps which keeps working in background. For example. Latitude keeps updating your location, if Sync is enabled, it keeps checking for gmail and syncing your contacts etc.
Also check Settings-->Wirelss and network --->Mobile Network--->Network Mode
It should be in GSM only and not GSM/WCDMA (auto mode)