You need to match the kiss with the circumstance. If you kiss someone and you attempt to put your tongue in their mouth and you run into a shield of teeth, then perhaps that isn't what they want. I have heard of teenage girls practicing kissing on each other. This is not a lesbian act. It is just educational.
Guys practice on things like bottles.
Of all the sexual problems there are, that is one of the better ones to have. That is considered appropriate etiquette. If the man reaches orgasm first, he might leave his girl high and dry. If your orgasm comes way after hers, then you might want to stall hers or reach orgasm more quickly. Try giving her less stimulation, try different positions, different rates of thrusting or taking a break and talking love talk.