I had this same problem a few weeks ago, asked this same forum, and here's how I got my first BJ.
Me and my gf had very sexual make outs (my hand usually under her bra or in her pants), but she hadn't blown me. What worked for me, is while making out, slowly guide her hand to your ****. At first my gf didn't do anything, but eventually she got the message and started feeling/squeezing it. At that point, just start taking off your pants and boxers. At this point my gf was jerking my **** while we were making out. I told her "lets just do one thing at a time", looked at my ****, and she got the message and started blowing me.