Watch the Dyads online guitar lesson by Christopher Woitach from Jazz Textures
Here's an exercise that I got from the great Mick Goodrick's book "The Advancing Guitarist", a fantastic book, full of "out of the box" thinking. This exercise uses 3rds and 4ths, horizontally, with the lower voice moving step-wise through a scale, and the upper voice creating the 3rd and 4th intervals. Try to practice this on all string sets, all keys, all scale types. Your fretboard knowledge will increase, and you'll have a lot more options for texturing your lines. The enclosed booklet contains many pages of linear intervals for you to try.
Much of my textural concept comes from guitarists Mick Goodrick, Ted Greene, Ed Bickert, Jim Hall, and Joe Pass. While I don't play exactly any of their styles, they have all been huge influences on my playing, and I recommend you give them a listen, you won't be sorry you did. Another big influence on me, and one of the very best textural guitarists in the world, is my friend and colleague John Stowell. He has some videos here on TrueFire that I highly recommend, if you'd like to really take your textures to the next level.