Jailbroken/Unlocked. What must I never do?

[wannabelean]

Other than

1. Update the firmware
2. Restore the firware
3. Use the reset settings. Should one not touch any of the reset settings? or do we just have to stay away from the reset all data and settings one(the one which restores the phone to the factory image)?

Is there any other precautions I need to make sure that I will never have problems with the JB/UL phone? I have an Iphone 3GS 16GB which was recently updated/jailbroken/unlocked to OS 4.0 by a guy on craigslist for a fee. When I had given it to him the phone had Iphone OS 3.0.

Also is there a way to figure out which method he used to do this job? He was using a mac.

Thanks!

[backstabin]

Just do not upgrade to new version until JB is out for that FW