This is what I do, it might help.
I study my reviews, and if I get 85% or more correct I add 4 more lessons. The next day, I do my reviews again, including the new lessons, and if I still get 85% or more correct, I’ll add new ones. If the 4 lessons I add seem very simple or already know them, or if my correct % is at 95% or feel very confident, I might add 8 lessons that day, or even more.
Then I repeat the next morning, or most days even review at night as well, and whenever I get to that % I add new lessons. In the beginning It was 90%, but I found out it was slowing my progress and just too difficult, then I did it at 80%, but I started adding too many lessons at once and it became impossible to learn, so I find 85% works fine for me, enough to get me motivated and have a sense of progress.
Find your own formula, and have fun with it.