Valkyrie: 8.5x7.5 is a bit larger than what I took myself the first time (roughly 8x6), but shouldn't be undoable.
Make sure you're wet enough - it's easier if you have come one or two times before (most, if not all women are multi-orgasmic, it's a matter of learning how to come once again after you've done it the first time). And when I say wet, it should be just that - almost in excess. Slippery and slightly oily to the touch, almost to the point where you have it running down your thighs... ;)
Your own lubrication is the best as that what's it created for, but I find that some extra just at the opening and on the tip of his penis helps when dealing with a larger one. A large penis sometimes get stuck on the skin just at the entrance and that's uncomfortable for both you and him.
Make sure you go about it slow so that you can relax and learn to accomodate the size. Try not to tense up - it will only make it harder for him to enter and will hurt for you as it creates friction and he has to push to enter you. If you're wet enough and relaxed enough he will slide in by just leaning ever so slightly against you or pushing ever so slightly up against you (depending on what position you're in).
Either put yourself on top so that you have full control and can decide when you want to stop. Or prop up your hips on a couple of pillows and have him kneeling just in front of you (tell him to take it slow). By raising your hips on pillows or sitting on top of him you create the straightest line possible for him to get into you. Doggie style or plain missionary position can be great, but not for that first time - the opening of the vagina will be slightly covered and a lot smaller than it need to be.
Last but not least - talk, talk, talk - tell him what feels good, when it hurts, when you want him to continue. Men are not mind-readers and if you're not vocal, he will have a hard time knowing whether he is hurting you or pleasing you.
And take the time needed, if it doesn't work the first time, have a go at it another time. There is nothing saying that you have to take all of him the first time around. Better take it slow - a couple of inches at a time until you're all the way there. It should be a pleasant experience for both parties involved.