Spice up your screenplay

I have been told not to use voice overs and flashbacks when writing a script. None the less I personally find the effective use of flashbacks appealing.I thought that it was just me feeling so until I found http://www.lindaaronson.com/ when reading the book "Genre Screenwriting" by Stephen V. Duncan. (Stephen's book is ok) Linda is great check out her blog and book - I find them interesting. I would like to explore more starting at http://www.lindaaronson.com/main/page_the_six_sorts_of_parallel_narrative_.html