most of the time a profile pic, and pedigree... along with a short desc of pos/ vs neg.. and what she needs wills sufice... Although I'm not a super god, like some people on here, I've seen my fair share of bulls- and as long as your cows are of the right breed- I'll give my 2cents worth.
One thing to remember is that, IMO the biggest mistake by most breeders is breeding a small number of cows, to a great variety of bulls... Now, I do admit that it's always our goal to breed +'s to -'s, and try to make the A+ calf... Basically, we all breed this bull to help this cow, and in a perfect world, that would work... however, on our planety, that doesn't happen to often... Mostly it seems that calves will inherit the negitives from both parents and be junk...
I don't know how many cows you have, what breeds, or what your goals are, but from the start, I suggest using bare mininum number of bulls... especially if your wanting to keep heifers, and build a herd- its better to be consistant instead of mixing and matching..
From personal experience, it's much more pleasing to the buyers if you have a uniform group of calves that are slightly above average, with one or two good ones in it, than to have 1 great one- and a bunch of Good looking steer! eaters. especially if your looking to create repeat customers