An easy way to avoid grips from getting stiff is to keep using them everyday, you know lol. But also, make sure they aren't wet when you are done from bars - if they are put some chalk on them before putting your grips away. Also, I have found that it helps to have them in a sealed/closed bag, and they get more stiff when more air gets into the bag. If your grips do get stiff, you just have to warm them up again with swings, not that big of a deal. But it's nice when your practice starts out with nice grips that aren't stiff and hard!