While a coach is definately the best way to go...
I recommend a self-examination of your game. Figure out the difference between your 200+ games and your 160ish games.
Is it an accuracy/timing issue? Is it lane conditions/transitions? Is it a concentration issue?
You need to figure out what is causing you the most problems and work on that one area.
Keeping a journal is a good idea. You can buy log books or you can just make your own. Write down a) where you stood, b) where you targeted, c) what you actually hit, d) what pins fell and most importantly your comments. (Off-balance/shoe stuck/ball choice/etc.) Then review the log. It will point out if you have accuracy issues or problems with certain spares, etc.
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Good luck & good bowling