Scared to suck dick

I've never done it before and i really want to but i'm scared i'll be terrible. i hear the best way is to curl your top lip over your top teeth and use your tongue as a barrier from your bottom teeth so no teeth are felt for his dick. but my mouth is really small and my tongue is really big so it doesn't seem possible. i also don't want to gag. so what do u guys think? is this technique even possible? are teeth a REALLY BIG no no? are there other techniques? what feels best for you? would REALLY appreciate advice!