Having scrimmage games will help on possible game situations. Practice also receiving balls from throws from short stop or 3rd base.

Make sure to have proper warm-up before games and flexibilities exercises after training or games.

Always be mentally prepared during training and games

http://www.softballperformance.com/softball-fielding/how-to-play-first-base.html

First base is my favourite position. You just always have to be aware of what's going on and be ready for any throws that might be coming your way.

First base is a great position to play and one of my favorite positions to play.
Practice recieving balls and getting to the bag. Also practice game like situations
like when there's a bunt or whatever many outs.Also be aware of your
surroundings too. First base is one of the most important postions because it's
where most of the outs are being played. But keep practicing and you'll get better
I'm sure:)

first base is the ultimate position it is by far my favorite i have played first base for 5 yrs and what i have learned is that you have to always be alert and ready for anything paly ur base and have communication