Regardless of your age, take down any pin-up posters of women or even men from the walls of your room, if you have any. Hide your dirty magazines. Hide any other things which could be taken as sexual in nature.
Most important, make your room clean and neat. Put a set of fresh sheets on bed and make bed in neat manner.
And the bathroom. Make it sparkling clean. Hang fresh towels. Put new bars of soap, one near the sink and the other in the shower.
Does your bathroom have a ventilator fan? Whether it has one or not, it's a good idea to have a room-odor eliminating spray can and place it prominently in front of a toilet bowl. (You know women sit, don't you?)
It would be a nice touch to have a new toothbrush in case she forget to bring her own.
Do you have another room you can sleep in? If you do, make an offer to her that you would sleep in another room and she can keep your whole room to herself during the night. She may say you wouldn't have to do that, but make an offer any way. That will give her the impression that you are a true gentleman (which you may not be).
Let's continue with our preparation.
After removing your dirty magazines (preferably OUT of your room in case she get the room to herself and possibly go through your stuff in the middle on night), put a few well-perceived magazines/newspapers, casually scattered around in your room.
Recommended magazines/newspapers:
National Geographic
Scientific American
Premier
Nature
Wall Street Journal
New York Times
Enquirer
We need a general news magazine:
U.S. News & World Report
We have to have a contingency plan then.
How many condoms should he have ready? (I guess he should hide them outside of his room, though.)
Should they be ribbed or smooth?
Oh yes, I almost forgot, a box of Kleenex. Yes, that's an essential item.
