Just getting some good rides in where nothing bad happens will help build your confidence back up -- I like one of the other suggestions about having a trainer or someone else you trust walk next to you for awhile, that would definitely make me feel better! I had a fall a couple months back and had to gain my confidence back up too, I was getting very nervous every time I would ride which was making my horse nervous! I ended up asking my trainer to ride her for me a few times, and seeing him with good rides started making me feel better, like "ok she's not going to bolt again like I keep thinking she is!"
I would start out letting him ride her for 1/2 hour or so, then I would get on and walk her around with him still in the arena with us. After awhile, the confidence started to come back! Also, another great tip someone else mentioned was remembering to breathe so that you stay relaxed...a good way to do this is to count your horse's steps...for whatever reason, it works! If you are counting out loud when your horse is walking or trotting, you are breathing in and out without thinking about it
Worked for me anyway! I was jumping one day and my trainer wanted me to count the number of steps my horse took before the jump...I had no idea why, but did it anyway...he told me later it was just so that I would remember to breathe so I'd stay relaxed!