The clear blue digital 'smiley face' tests, from what I can remember, work by using FMU once a day a few days before you're expected ovulation date. After a few days' use, they kind of lock you out, as in, you can only use them a few mornings month before they stop giving you a reading, then they sort of time out for about 28 days.
For that reason, I used Internet cheapie OPK sticks from the day after my period, using FMU and about mid afternoon (apparently that's the most accurate time to catch a peak) throughout the cycle, using the digital as the tests got darker to pinpoint impending ovulation more specifically.
Having said that, for about a year or 2 prior to TTC, I tracked ovulation via monitoring by BBT and changes in cervical fluid, and I would 100% suggest using these methods alongside the OPK's to help identify a baseline.
So I would use cheap OPK's every day, then digitals nearer to what I thought was impending ovulation, then BBT every day to confirm ovulation. This is because, although I had a period every month, my ovulation date varied due to PCOS, shift work etc. It helped to be able to see on my chart that, when TTA, my period wasn't 'late' I just ovulated later that cycle, and when TTC, when to time sex. From this, I learnt that I ovulate every month, usually about day 18, and my post ovulation phase is long enough and healthy enough to support a pregnancy should it occur.
We conceived first time, both times. Sadly miscarried our first pregnancy at 6 weeks, but now have a 7mo baby boy.