Missionary would be the optimum first time.
Kiss her for as long as you can beforehand, during and after sex. that will make her wet, show her that you care(hopefully you care) and make her want to do it again.
dont expect a lot of sex the first few days cause she is going to hate life for the first few times.
Bring a lot of lube, you sure as hell dont want a broken condom the first time you fuck.
if you can't come the first 30 minutes you should stop and and either ask her to finish you off or just go to the bathroom and do it yourself cause less pain for her= more sex for you.
And most importantly don't forget to lie to her afterwards by telling your fat bitch that she is beautiful and that you love her.

Take piks and post them afterwards.
Good luck