Part 2 of response-

Pushing limits safely is one of the appealing aspects
of our sport...once one can actually stay up, this
progression seems to be...

1.) How long(duration)
2.) How high
3.) How far
4.) How fast

(How low) seems to fit in there somewhere...but it
can bite harder then the others. One drill I was taught..figure
out what the sink rate might be for a particular day
if you hit the wrong part of a thermal...at a safe
altitude pop your spoilers to that sink rate...then
start circling to learn how much altitude you loose.

As with many learning guidelines...the best instructors/mentors
can relay this sort of information in a non-confrontional
tone...which may aid learning. Sometimes RAS is lacking
in this area