Here's a few
Learn as much as you can about weight training, read from as many different sources as you can, use what seems logical and test them in the trenches.
Don't get stuck on what one particular guru preaches because as much as he/she knows he/she will not know everything.
Obvious but many ignire this one; if you get pain (the bad kind) from doing a particular exercise in good form subsitute it for one that does'nt cause pain, Ignoring it will not make it go away.