As has been posted, heat detection is the single most crucial elemnt of succesful AI. We use a horny steer, but painting the tail head or K-Mar patches or some of the newer silver looking scratch off patches work good too. A half hour morning and evening is the minimum. Looking in on them during the day also helps. In many ways it's like calving. Noticing anything that's unusual behaviour for that animal, looking for swelling of the vulva, etc. I just bred 2 heifers for the neighbor that showed no active signs of heat, no riding, chinning, being ridden, nothing. He saw the vulva swelling and when I bred them the mucus poured out and the cervix was so open you could drive a truck through it. After breeding a couple of the other heifers came over, sniffed them and wandered off.
After heat detection the other elemnts are all equaly important. Quality semen that has been properly handled through out it's span from collecting to deposition in the cow, proper deposition and placement, cow not overly agitated, experience, patience and cow side manner.
dun