~20% per cycle. The ideal time to have sex is 1-2 days prior to ovualtion. Doing so would probably yield ~20% chance of conceiving each cycle (lower with advancing reproductive age), ~50% chance conceiving within 6 months, ~85% conceiving within one year. If not pregnant by then, recommend seek infertility evaluation.
Increase pregnancy. Having sex with a fertile partner multiple times around ovulation using sperm friendly lubricants (if needed) will increase the chances of conception. If you've been doing that for over 6 to 8 months without success it's time to have a fertility work up. Most women will conceive within 6-8 months of trying.