I'll cut to the chase; there is a simple change to your bowling action that is a big hitter in fault correction.
Straighten your run up.
You see, when it comes to technique, so much that goes wrong can be traced back to an earlier point. That's why batting coaches focus on the grip and stance first, and it's why your bowling coach should look at your run up before he starts with the "business end" of the action.
Of course, a straighter run up will not fix everything, and there are exceptions to the rule. That said, there is plenty that can be done without ever worrying about 6 months of corrective drills and rebuilding your action.
So, spinner or seamer, Here are some of the things a straighter run up can correct: