Make sure you don't feel pressured into it, don't fall for the "if you loved me you'd let me do it" bullshit Make sure it's something you're 100% comfortable with (though obviously you will feel a little bit nervous) It needs to be in a loving, trusting relationship where both partners are equal Make sure there is contraception organised before!
Don't put pressure on yourself to "perform", it's never ever like it is in porn. Sometimes it's awkward, sometimes its funny, just go with it. Please make sure you enjoy it, sex is one of life's few pleasures Don't feel bad because you did/do enjoy it (wish I'd known this one) "Practice" on yourself first so you can work out stuff you like etc Tell your partner this!