when you reach that point, the salvia world is very near. have a very big toke, hold it and before you release it, put your head back and close your eyes. remember that the most important thing is that you are alone and no one will see you (this works for me).
some people have more resistance than others...yesterday i needed to take about 6 10x puffs, because i tripped in my car, and i stopped at the shade of a tree. the cars that kept running by would not let me trip. it was funny, though. i almost had no visuals, but the thoughts that salvia gave me were at first hilarious, than they were very real.