Dave Tate has a few articles on this site about accommodating resistance and setting up conjugate cycles(The Periodization Bible Part II). His article on accommodating resistance lays out exact percentages for beginners, intermediates, and advanced lifters for DE work with straight weight, bands, and chains.
Typically when Tate or Louie are talking about beginners, intermediates, or advanced lifters they are saying that in regards to Westside...not lifting in general. I believe Tate has classified beginners as someone who has used Westside a few times or not at all. A bunch of people think that DE days on Westside just means taking bands and adding them to X% bar weight...at that point they've gone full on retard.
It is widely suggested by most Westside experts that bands should not be used for beginners, and when they are used with intermediates or advanced lifters they need to be cycled very carefully. As you probably know, bands are extremely taxing on the CNS and the body in general.
A nice option for a beginner might be to use straight weight for one 3 week wave, chains for the next 3 week wave, and so on. The best thing you can do is go into the authors section on here and read Tate's article on accommodating resistance and periodization.
Also, you may be aware of this already, but traditionally DE work for bench is done with triples, squat DE work is done with doubles, and deadlift DE work is done with singles.