We guitarists use our hands. We fall into patterns. Now sometimes that's a good thing. But if you want to be original, sing it. It takes away your finger patterns and muscle memory and forces you into uncharted territory and new licks.
Begin with something slow and think whole notes, then move on to 8th notes. Change the feel and work with triplets. End on 16th notes or faster. Create a build. Tension. Or just stick to a main pattern and keep coming back to it.
Decide to only use one string for the entire solo. It will force you to phrase and think differently. Or limit the notes by NOT ever playing a root note. Limitations are freeing!
Who says a solo has to be made of notes? Play a solo using a chord pattern played rhythmically or even insanely and dig the craziness. Or if it's a slow tune, enjoy the beauty of chord on chord playing. Or use these as arpeggios. I often think of chord on chord when soloing.
What would a sax sound like? How would a sax player solo? Or violin? Or piano? Or drums! Or spoken voice?
Maybe you shouldn't even play a solo. Or maybe it should be so minimal that you can barely call it playing. But if that's what the song needs, put your ego aside and let it be. I have done this numerous times. And not due to laziness; due to its being what is appropriate for the song.
Pick a hero. Someone you emulated and dreamed of being when you first started playing. You can never fail. (Unless you are playing on a rockabilly song and your roots are Yngwie Neo-classical. Then, skip this step ... forever!
Why not try something you've never done before? Do the most ridiculous solo. Play faster and sloppier than ever. Make a statement. It may just work in the right situation. Or play another song melody. Or play something that sounds like a whale. Use only the low strings as high on the neck as you can! Just the act may free your mind.
Try playing using dissonance as opposed to a melodic solo. Use as many outside tones and unrelated notes as possible. There is an ugliness/beauty in this type of playing, and once mastered it can be a friend. By making the solo sound uncomfortable, you can then shift into melodicism and make the notes sing. The dark-to-light shift does magic.
Imagine you are making a movie instead of a solo. Start on a wide shot. Maybe long flowing notes. Then add a motif as a character. Repeat this motif and think about playing it over the wide shot long notes. Add details to the story by developing the line with more notes and rhythms. It's still just a solo, but in your mind you are making a movie.
I hope these concepts help you the next time you are stuck for an idea on what to play.