If you look carefully Duolingo will recommend which unit you should do by highlighting the button. Duolingo recommends the strategy to jump around which I myself would recommend. I find that if you try mastering a unit before moving on, you are not really learning but memorizing the answers.

My personal strategy has been to move on as soon as I unlock the next level, and if I feel like I'm starting to get stuck, I go back and get my mastery in those modules by translating sentences. It seems to be working for me pretty well so far.

I just saw that I completed an activity in Basics 2 and because it had basics 1 stuff in it, I got 10 points for both basics 1 and 2