The first tip is going to be to knock down any texture or loose compound or tape within your work area. Get out anything that doesn't have adhesion with the drywall
Second tip is to go to your local PPG paint store and get a can of this, and use it as directed. Using this problem surface sealer may save you big headaches in the future. This can also be used before paint if the surface is unstable.
Our third tip is: Prefill any large hole or crack before taping.
This will allow you to knock off any sagging joint compound and allow you to tape over a perfectly flat area allowing for a much better repair.
Drywall Repair Tip #4: Use many light coats of a mid weight joint compound to finish the repair area. This will allow for a lot less sanding.
Drywall Repair tip #5: Have FUN and STAY CLEAN.
Cleanliness is everything if you expect a good DIY drywall repair.
Wash yourself and your tools often.
