As a guy who takes care of about 12 track cars on any given race weekend I can tell you the average driver has a LOOOONG list of stuff to worry about before messing with heel&toe techniques... There is no real advantage to rushing to shift fast in road racing, it usually just tears up cars and drivetrain parts. My personal technique is to roll off the throttle and push the stick to neutral, then push the clutch in and put it in the selected gear. By moving out of the gear without the clutch you automatically get a "blip" and the gears all spin up, then going in to the next gear they click right in. It also forces a smooth shift.
But there are 30 more opinions or more on this than people on the internet..
Good luck!
Dave