go to the driving range - take your 7 iron and pw only. go to the chipping green and spend 2 hours there for 1 a week for 3 weeks. you can make the check out to rononeill.
seriously, find someone, not necessarily a pro, who has a decent short game, and ask for a few pointers. then practice it.
if you watch someone shooting in the 80s and compare their swing/game with someone in the legitimate 90s/low100s. there is very little discernable difference. its the # of disaster holes and short game that set them apart.
if youre shooting around 100 that means youre roughly double bogey golf w/ a few bogies. how many of those shots are within 100 yards? be honest
unfortunately, the short game is the crappiest part of the game to practice - it is, however, the most rewarding.