I got a new monitor and while it's just a TFT screen, I'm wondering weather there's a rule of thumb as to how much brightness and contrast there should be?
how do you guys decide do you just mess around with it until you thing it looks good?
Its quite a broad and relatively complicated subject but basicly:
You should callibrate your screen to a gamma of 2.2 and preferably at a whitepoint of 6500k.
If you monitor has an sRGB profile build into it, just choose that and run a monitor calibration program.
Just do a quick google for 'monitor calibration'. You'll find tons of info and tools to help you callibrate your screen.
If you are going to do some graphic work on your computer this is verry important and then i'd recomend you to get a hardware monitor callibrator. Such as the 'spyder'.
http://spyder.datacolor.com/