If you're too long for her:
Know how to fuck in doggy style without causing her to flinch by short stroking, if she's not into that kind of pain.
Know which positions are best for a penis that's longer than a vagina.
Know how to play with her clit while fucking her.
And if you're girthy:
Know how to take it slow the first time, with lots of foreplay.
That's all stuff that's specifically big cock related, then you need to have some skills in bed, like know how to kiss, how to talk, how to show passion, how to touch her body, how to go down on her, how to kiss her earlobe and her neck, how to read her responses to you and replicating what you did... Things like that.