Rachel,
I have found that it is mostly trial and error.  It's different for each person for each food for each day.  When I first started trying Lactase pills, I got very sick.  I was convinced I'd had a reaction to the pills.  It took me over a year to try
them again.  I would definitely recommend starting very slowly with food low in lactose.  I found that I have to take the maximum amount of pills.  Also be aware that it's 1-3 pills per serving of lactose.  The amount of lactose varies between foods
and is more processed in some foods than in others.  Keep in mind your body has not had dairy in 10 years, it will take time to adapt.  I have also found that there are days I can eat dairy with the pills and days that the pills don't help and I
still get sick.  Also, there is a limit to how much the pills will work for me.  I can't eat dairy at every meal and expect to feel okay.  Consider your schedule before trying anything.  You don't want to experiment right before an important meeting
or when you are watching 10 children or something like that.  Good Luck!
Catharine