What can i do to prevent premature ejaculations? -
1) A desentizing cream or lotion, but be advised that it can transfer over to the woman and cut her pleasure as well.2) Change of position. One that does not offer as much stimulation as another.
3) Understanding the signals tha tyour body gives, so you can slow down, back off or stop altogether.
4) There is a book out there called the Squeeze Technique witch helps in delaying orgasm, but I may not have the title right.
Masturbate on your own. Try not to ejaculate so quickly each time. Stop when you know you are going to. Beleive me, when you hold it off a few times it is soooooooooooooo worth it when you actually let yourself go. If you keep this in mind in could help also.
Tell the guy your having anal sex with to slow down a bit.
use condoms +lots of lube
Stop wanking