The best rule of thumb is to have sex every 3 days
I would start testing for ovulation. The apps never predicted my ovulation right so I never relied on those. When you start getting close to ovulation start having sex, then have sex the day before/on/and after ovulation
Everyone's cycle is different! There are apps to help you figure out when your fertile window is. Also taking your temperature every morning or using urine LH test strips helps to figure it out with more specificity than guessing based on your cycle.