If Ron Clifton comes to your area to do a clinic, it is worth the money.  3 days, no more than 8 bowlers, and small changes.  He video tapes each bowler, lets him/her know what he sees, then gives a drill to start with.  Once he has finished with the initial, he consistently watches and revises as needed.  No cookie cutter, each receives individualized instruction.
--------------------
USBC Bronze Coach

"I cannot change the direction of the wind but I can adjust my sails to reach my destination." Jimmy Dean
Quaker 10/93 - 4/07
Quaker

I am actually going through this myself right now.  I making drastic changes to my game from many angles.  You have to decide which change to make first and master it.  Then on to the next and so-on.  Practice practice practice.  You cannot decide to make a change and throw a half dozen games and be ready to do it every time.  For my summer changes, I expect to throw about 1000 games of practice to get where I want to be.

I compare bowling to golf a lot because they both require a lot of body motions to come together at a specific point with specific timing that has a near 0 margin of error.  When I made 2 small changes to my golf swing a couple years back I estimated that I hit 20,000 practice balls for each of the two changes I made to get to the point where I could repeat it on demand.  To this day, I still revert back now and then and the result is hideous.