Any tips to prevent loose skin?

I am just starting out, and have over 100 pounds to lose. I know that alot of people have loose skin after losing that much weight, but I was wondering if there is anything that I can be doing along the way to help prevent it. Of course there is no way to tell yet, but I am guessing my problem areas with having loose skin will probably be my lower stomach, my upper arms, and my inner thighs. Are there certain exercises that I should be doing, or creams, or anything?