There is an article on this on the Home Page..

The easiest way is for you to lie back. Have a big pillow or cushion (or several) behind you so you aren't exactly flat on your back and to support your head. You can cross your arms under your breasts to lift and push them together. He can thrust slowly or you can wriggle and rub against him. Another technique is for you to lift and press your breasts together over his penis with your hands. While his penis is between your breasts you can do a slow juggling motion, lift and lower them along his shaft or squeeze them tighter and loosen them repeatedly. You can also combine these. If his penis is long enough you might lick or the head as it approaches your mouth or even take it into your mouth. It is an incredible turn on to tit fuck and be sucked at the same time.
Some guys like to blow in or at the mouth or the face in general. Others prefer to shoot at her throat adorning the woman with the famous pearl necklace. Other times it is good to just feel and see your penis buried beneath a luscious mound of breast flesh.

It is often more enjoyable to both man and woman if some sort of lubricant is used. I like oiling my wife's boobs up before plunging my manhood into her cleavage. If you are considering his penis entering your mouth you might want a flavored edible lube.

I have done all the positions described in the article plus a few more. What I described is what I did my first time and I still consider it one of my favorite orgasms of all times-and it was 22 years ago-yet I still remember vividly. Your guy might like having you kneel over him or on the floor before him as he sits or stands. It's all good, especially if you are a large breast fan and have a nicer pair offered.

I hope it goes well for you. This is precisely what I expect to be doing in about 90 minutes.

Cheers!
dlb

Everyone is different re: comfort and ease of positions .. I suggest you just try
and see which one or ones suit you