One of the worst student habits I see late in their training (CPL and CIR) is poor attitude flying. Remember lessons 1 and 2?
POWER + ATTITUDE = PERFORMANCE!!!!
Don't just turn/descend/climb the aeroplane without looking outside at the nose attitude you've just selected. Same applies to flying on instruments - the AI (or AH to some) is your friend - don't change flightpath by scanning the performance instruments only - DI, altimeter etc. Learn and set the correct attitude first, then check, adjust, retrim. Practice this basic skill while building your 10 hours instrument flying leading up to the CPL.
A poor bit of advice is 'you should always be doing something on a nav'. Sorry, but that's bull****. If you're ahead of the aeroplane, completed the CLEAROF checks etc just fly the damn plane. Guess what? You'll fly more accurately and you'll see more ahead and around the aeroplane. Your passengers will thank you for the accurate flying later on.