Specific exercises or drills to improve?

have some interest too

You can find a pretty nice list of dart games here https://darthelp.com/games/

We don't really have many drills. But some of those games are great for certain goals. Like Bobs 27 for doubles or Mulligan for triples. Most points-based games will help with your high triples while still keeping things interesting.

I practice a lot of doubles around the world. I force myself to finish in less than 25 turns. My best is 19. If I throw over 30 it is a very bad day. (We all get stuck on a number now and again.) 

I play a lot of 101.  Give yourself 101 points and 6 darts to take it out. If you fail, begin again. This was based on a bar game called 50.  Each player steps to the board and tries to take out 50. It costs a quarter to throw three darts. The first person to take out the 50, scoops the quarters. 

Here is a thought for you regarding practice. Most people focus on their top game. Trying to hit 180 or big numbers. Spending the same time working on the low end of your game can result in amazing improvements. How many darts can you stick in a fat 20 before missing?  Getting deadly consistent at just hitting the 20 can demonstrably improve your game. Now, try and get ten 10, or 20 darts, in every cricket number. Nothing can help a game like consistency. 

Posted by: @wookyuk99

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Besides regular games like 501 and cricket are there any exercises or drills that people do to help improve accuracy?

Also sometimes I find myself getting distracted or losing my rhythm. Are there any mental exercises or techniques that you use to stay focused and in the zone?

thanks

The ABC....  When you get to your setup position, say 'A' in your head.  The draw back is 'B.' and 'C' is the release point.  Get the three points locked into your head. (This is point 'A.'  This is point 'B'.  This is point 'C.' This is called 'Anchoring."  It's a useful technique.