Really depends on what aspect you want to focus on. You are at the right place for drills. My suggestion is to check out Weplay's library of softball drills and use the ones that suit you most. For me soft toss and tee work for hitting and infield hitting with 3-4 players is about as fun and effective as anything. At the tee you can see hitting mechanics problem and fix them and taking infield you can see fielding and throwing mechanics and fix those too. Find what you like keep using it, compete, and have fun doing it.

Coach Jones

Make sure to have drills focusing on all aspects of the skills in softball. Have drills on fielding, batting and baserunning. Then have a program on conditioning to compliment your skills then progress to agility and speed training. Flexibility is an essential part of this process. Add visual training and mental toughness exercises, this may help you have that edge. Don't forget to put a rest day for your muscles to regenerate from all the activities you've done.

http://www.softballperformance.com/what-is-softball-specific-training-exactly/