It's a very difficult question to answer.
If you have irregular cycles and don't know when you are ovulating, BD'ing every other day might be a good idea or at least every couple of days.
However, if you have regular cycles and know when you ovulate, then you can time your BD'ing for the few days leading up to ovulation and the day after. I did this with my son and got pregnant the 2nd month of trying once I knew when I ovulated.
My cycles are not so regular after having my son so we are BD'ing every other day at the moment.
A friend of mine got pregnant with both her kids just by BD'ing once in her cycle.
What works for one couple might not work for another...
If you are TTC, best to start taking folic acid now.
Good luck!