I've found that the first time should be done standing up, so get on a pair of high heels (come f*ck me shoes I'm told) and stand facing up against a wall, get relaxed use lots of lube get him to put one digit in, then as more as your able to felll comfortable with when your at the point of feeling like your too stretched let him get in there. The best thing about standing up is (and this may vary depending on the hight difference), he will not be able to go buck wild do too much damage since you'll be ablr to go up on tip toes when the pressuer is too much, also put a towel down somewhere for easy clean ups. Have I grossed out anybody yet?!