Rollercoaster close-up (spintop: Duncan
Rollercoaster to hand (spintop: customized Hollow Point)
Roller-coaster to string
First learn the general mechanics of the trick (drop, slide, pop) which are not difficult. You should be able to do around 5 rollercoasters to hand from a boomerang throw without regenerating. Then you have two options: a) try to extend the number of rollercoasters to hand, learning to regenerate by adjusting the position of the top and the timing of the jerk; or b) learn to lasso consistently from the pop, worrying about regeneration later. Use a heavier top to learn, such as the Hollow Point.
Heavier and larger tops are generally easier to regenerate. There are several reasons for this: 1) they spin at a slower rate so it is easier to achieve a string velocity greater that the speed at the surface of the tip groove (i.e., friction force accelerates top); 2) they precess slower so there is more time to do the trick; 3) they have greater inertia against which you can apply more pull; 4) they are easier to catch with a lasso. Good tops are (starting from the best) the Hollow Point, Trompo (Spintastics), Gates (YoyoJam, discontinued) and the Rip Cord (Duncan).
Some players lean the top quite a bit while doing rollercoaster to string, so the catch is almost like that of sewing machine. This facilitates the lasso, especially for mixing in some behind-the-back catches (or doing the whole RC behind the back). However, I prefer to pop the top upright for normal rollercoaster: I think it looks better and makes the trick more distinct.
Important: the string can make a big difference. A string too soft is bad. Use a new, clean string!