All of the above. I'm an advocate for knowing your body and cycles, but the withdrawal method/rhythm method are not very effective if you are not wholly in tune with your cycles. Very few women these days are.
Get on the pill, the Patch, use a condom...or just don't have sex.
To avoid pregnancy, use either condoms, the IUD, the Pill, the shot, or the implant (is that even still around?) Do not try to guess by the calendar, do not try "pulling out." All you will get with the last two approaches is pregnant.