Another thing to try when creating a blues insrumental is watch for the chord changes and shift your pattern to correspond with these changes.

Example Em -- Em Pent Blues , Am -- Am Pent Blues Scale, BM -- BM Pent Blues


I also recomend learning as many turnarounds that you can.

Also start a song with a turn around. "Queen Bee" by SRV is a good song that displays both of the things I have mentioned.

Also to mix it up a bit play a Major Blues scale instead of the standard minor Pent Blues. It has a a unique sound that still works with the minor chord progression. This usually works best with slower songs but ther are no rules.