Make sure the fleas are taken care of as they are commonly the cause of this skin irritation. I would use Frontline or Advantage for this because it kills the fleas when they jump on you dog. If it is not flea related you need to see a veterinarian to find the cause.
My male Boston had a hot spot once and my vet told me to get over-the-counter anti-fungal creme--like for athlete's foot, and rub it in good everyday-generic brand works fine. Rub it in about twice the area of the hair loss. It takes a couple weeks, but the hair comes back in, no problem. It worked great. Hope that helps.
Clip as close to the hotspot as you can, the more hair and scabs removed the better. Give it a good scrub, plain soap is fine, rinse off the soap well. Dry it with a towel, just pat it dry. And apply an antifungal oint everyday till its gone. You could probly get away with useing polysporin too. Also don't allow the dog to lick the spot, so you may need a cone.
goldens seem to have this problem a lot. Rusty will chew on the back of his hip. Vet said it was mostly our very hot and humid climate. Anyway, all the suggestions above sound good to me. I've always gone to the vet, but next time I think I'll try those instead. Anyway, I just wanted to mention that to keep him from biting or licking it when I put the medicine on (and to keep from having to get a collar) I put an old T-shirt on him. I put his legs through the arm holes and pull it back far enough to cover the spot and then tie it up in a knot so it doesn't drag. Works for me. Good luck!