Girls I NEED advice about BlowJobs

Ok so I'm in my 20's and had never slept with a guy until now. I've always been with women, I always said I was a lesbian but now I am dating a guy and we have great sex so obviously I am not a lesbian, I'm bisexual. But I am absolutely Terrible at giving BJ's ...I have a gag reflex which sucks lol I have no experience at all! Any tips ?! I need advice girls...I wanna please my man in as many ways as he pleases me ;)