Working with threaded fittings

Can anyone share any tips and tricks for working with threaded fittings? Household sizes, like 1/2 and 3/4. One thing that comes immediately to mind is backing up on a pipe for its final position. Say you tighten a valve too far and the handle is out of alignment. Is it best to take the entire thing off and start again or is loosening appropriate to find the final position? How many threads should be sign on a properly torqued fitting for the different sizes? Is there a standard with NPT? What about wrench sizes? anything and everything you can think of to make this easier for me would be much appreciated.