I nursed both sides each time, but I would try to alternate which side I started first (since she would drain that one the most). Honestly, I would just feel my boob to see which one felt most full. I offered that one. lol.
In the beginning, I did like to time how long she would sleep for and stuff like that at night, but that was just to see how long it took her to space her feedings. I never woke her up at night (after that first week, anyway).
During the day, I fed her every three hours and I would either use the timer on my phone or just watch the clock. I tried to do it on the hour, so it was easier to remember. I don't think I ever fed her less than every 3 hours during the day. Then, when she started eating solids, it felt like I was CONSTANTLY feeding her either milk or solids.
DD1 started STTN around 7 weeks.