I normally always double clutch, and when it calls for it heel toe, as it does make changes down smoother, keep a more balanced car, means i can go into first at up to about 50 km/hr smoothly and without any gear damage
. When coming into a high speed corner, i usually will stay in what ever gear im in untill i reach my corner speed then change down to what ever gear is appropriate.
On the street i always try to practice it, though obviously without speeding, just driving normally. I dont bother double clutching on upshifts. just let it fall in, and do the clutch as quick as possible, sometimes without