Flying on instruments is really is the same thing as flying Visual...that is to replace the big world outside with the little one inside (AI) and the same rules apply, but are smaller and harder to notice. When the attitude is stable and trimmed, you should look away from the AI to other instruments or do other checks for only just enough time to see what you need to observe, then back to the AI, again for just long enough to observe what you need. Make power changes by feel and sound, then when trimmed on the AI, scan to check power and fine tune it. I also recommend:
Move HDG bug or CSE before rolling
All changes on the AI, slowly, set, lock, trim and look.
Trim all the time even at low angles of bank.
When looking away from AI, think: 'priority', and 'next event' that will occur (eg: arrival at HDG, ALT, IAS target etc). Prompts like this assist if you are having trouble missing items when busy.
Often slow scanrate is quoted as being a trainees problem in a busy IF exercise. My view is that technique is of much more importance - if you do not trim and balance well in IF the fastest scan will not help you much. ALso scaning very rapidly is of no use if you cannot see the trends occuring. So make changes on the IA slowly and trim carefully is the key. Think "priority' (HDG, IAS, or whatever) then prepare for next event.
THe old hands will often say they 'just look around' rather than scan - they are really recognizing patterns and until the newbies have this expertise they need to work on techniques. Remember, you only need to look away from the AI at what you are trying to maintain or achieve at the time.
ILS: Closing C/L think: HDG change (Bank-ON, OFF, wait.) Avoid just rolling toward the CDI, otherwise you will ocillate down final.
VSI: ROD=5%x G/S, constant pitch on AI when settled, tiny changes.
Next event - check ready
Arm's advice is spot on. Relax, trim, prioritize and prepare for events ahead.
RM