Here's a drill that I use with my boys; regardless of age, I think this is good drill.
If you throw from 60 feet-move up to 35-40 feet and throw. Once you have thrown 5 strikes in a row, move back 5 more feet. Keep doing this until you get to the full distance that you are used to. The key to this is, don't change your velocity-keep it the same. Once you change your velocity ithis drill won't help.
Something that may work is to count the total number of pitches it took you to get to the game distance, then try and improve on that number each time you do the drill.
Sounds simple, but it does help.