Having your knees close to the chest gives more access, but might feel like it takes more effort, so find the angle that feels best to you. You will want to use plenty of it — and it needs to be a good quality anal lube. Did I mention Lube?
Sex Positions For Anal Play - 50 Variants With Pictures
Anal sex, however, can be safe so long as you are engaging in safe and protected sex. Make sure you use a good quality oil, and go for scents that are going to help you relax as well.