@Yeldar, for frequent small improvements, repetition helps.
You know how on one run you get a lucky perfect lap on say zone 42, and on a different run you get a perfect lap on zone 46 but crash on zone 42. Well with repetition you're hoping for that 1 time to get perfect laps on both zone 42 AND zone 46.
This is good for high zone scoring courses like the pure four: you know you can get perfect zones at really high levels, but on each run its at different times. If you do enough runs, sooner or later you'll hit that perfect one where everything hits (like the lottery I guess )
The only problem with this I get is my eyes start to bleed after like 3 runs :O So I have to take a break.

But to make big improvements I feel you have to really know the course. Notice how the corners flow at low speeds, how easy it is to get round if you use the right line. Stick to the line, even at low speeds when any way round will do, to drill it into your head. Then as the speeds get higher it will come more natually.