work on longitudinal section first, then cross section
if you have to fill more than one gap in a segment: don't click on each gap ! => left click and hold and drag over the gaps.
work on a level that is right for you, and never ever give up, great rewards will come! I got that when I was feeling very demotivated on the lightning tutorial. Got 4 right then one wrong, so many times. but now I am substantially more patient!