For each race you can gain up to 16 points for coming 1st, with the amount of points gradually decreasing the lower you place.
Once again, the requirements are increased and in order for you to unlock stage 8 you must gain 80 out of the 80 points available, in the five races you can play in stage 7. This can be achieved by five wins which will bring you to the 80 point mark.
Always aim to perform as many tricks as possible to give yourself an edge or more importantly even be able to keep up with the competition, but make sure you can these without bailing as that will seriously hinder your chance of achieving first place.