Get in position. While it hasn't been scientifically proven, it's generally thought that positions which place the sperm close to the cervix are more conducive to pregnancy, specifically the "missionary position" with a pillow under the woman's hips. Remaining in bed for at least a half hour after intercourse may also increase the chances of sperm reaching the egg.
UDPATE: If you are intending to get pregnant (and you're married, of course) you are allowed to remove the holy trinity IUD for that particular occasion. But remember - doggy, lotus, reverse cowgirl or any other unholy sexual positions are by all means verboten.