One of the things that hangs people up technically is playing on adjacent strings. It's much easier to play phrases that contain two notes per string than one note per string. Consequently, guitarists tend to avoid playing ideas that force you to play across strings. You will often see players stretch five frets to play a perfect fourth when there is a perfect fourth at the same fret or one fret away, but on an adjacent string. To be sure, it is challenging.
Just imagine the things you could play if this were easy. I bet it would change the way you think about improvising, and open up many new posibilities for ideas. This would be a good thing, no? The way you go about making playing on adjacent strings easy is practice. In fact, this is the kind of practice that just requires repetition. You don't really have to think about it very much, just do it. While watching TV? Sure. That's the level of mental capacity we're talking about here. But the benefits to your playing will be great. Here's the routine:
Play the first measure between the B and E strings first. Then move the exercise to the G and B strings, followed by the D and G strings. Play the second measure between the E and A, and A and D strings. When the notes fall at the same fret, use your middle finger to play the lower string. It might feel weird at first but it will keep your left hand in better position. Don't play them with the same finger, you might harm yourself.
Practice this with a metronome at quarter note = 100 or slower. Transpose it to different keys and places on the neck or you might lose your mind (and that of anyone in the vicinity).
*As with anything you practice, repeating the motion without worrying about the immediate results is what does the trick. *
Now do the same thing with fifths: