the thing about blues is: there really arent any rules. as long as its rocken, its the blues. i mean it sort of has one rule and thats the skeleton, thats how blues work. ya know 1-4-5, or as i like it E-A-B
as long as you workin in that format GO FOR IT. and "it" being anythin. i mean the class blues will do a lil riff at the beginning, like muddy waters does. You could also have a lil drum bit like la grande by ZZ Top. Chuck Berry is blues almost all in the blues format, and he usually does a lil guitar riff at the beginning of every song. so just go for it.
good luck and rock on
Aaron