My tips are:
Always use a condom !
Use a gel like K-Y and not Vaseline
Go slowly at first and find her comfort speed
Make sure Mrs Fry is relaxed enough to go ahead. If she's nervous or uptight, it might hurt
You could try a vibe or dildo first before you go in, pref ones that are smaller than you are to work your way up size wise.
I found the spoon position best for the first time as you don't get as deep penetration as doggie.
When you've done it a few times, she might like to try DP with you and a vibe/dildo...very nice !
Most of all, relax and enjoy !
having a warm water enema first can make it much erm... cleaner...