This is a very,very vague question because it really depends on a number of things.
A single digit handicap golfer will be looking at completely different things to fix vs someone who can't break 110 regularly.
You probably need to post your swing and/or describe your misses and and we can fill you in. Brian has always advocated fixing the face and it's common to look at the grip at the address position and where the face is on the backswing, at the top, on the way down and at impact. If you've seen Never Slice Again, the Twistaway concept is there to 'dis-allow' the opening of the face at almost any time of the swing. Often the student makes many compensations based on the how open/closed the face is.
Every golfer has their own issues, so the advice you are going to get is what has ailed another player in the past. That may, or may not help you. I suppose instruction would be a lot easier if we all made the same mistakes, but this isn't the case.
Erik