The salary chart is helpful to me. I export it to Excel and lay it out, and see what room I have this year and in future years.
I never overpay for a player. I rank them by "bang for buck" value by taking their salary request divided by whatever arbitrary rating I give them. Obviously, don't pay top dollar for some guy who always under-performs his ratings.
I never pay ginormous chunks of my total salaries/cap/budget on one player.
If I have plenty of cap space I'll take a gamble somewhere.