I think a log of dogs become fearful of bath time because of bad experiences with soap, or water that is too hot...
I figure dogs like cold water, So i shower my dog with water that is closer to 85 degrees (as opposed to the 105 i prefer)....
Another is soap in the eyes, If your dog associates stinging pain with the shower, hes gonna hate it. I bought special puppy shampoo that has no-tear formula so if it gets in his eyes its no big deal, just flush em out and it doesn't hurt. I also give him lots of treats and while he's never guna beg for a shower, he doesnt resist, Hes very calm and complacent in there.
Make sure you're down with em, and give em a really good, nice massage while all the soap is on em.