Your chances of conception are best when you have intercourse just before ovulation and/or the day of ovulation. Your cervical fluid is thus one of your best signs to indicate when to start having baby making intercourse since it offers a sign that ovulation is approaching.
You should begin to have frequent intercourse (at least every other day if there are no known sperm issues) from the time you first see fertile cervical fluid. If you do not observe fertile cervical fluid for several days, start having intercourse even before you see it. Ideally, you want to have healthy sperm waiting in fertile cervical fluid when your egg is released.
Also, make sure to look at Fertility Friend's "Fertility Analyzer" to help you time intercourse. It will take into account all of your fertility signs from both your current and past cycles if applicable.