This is a huge subject. In fact, I would suggest dedicating a year to not buying guitar CD's but recordings of other instruments. Sax, piano, trumpet, xylophone, zither. Part of what will make you stand out as a guitarists among other guitarists is if you don't sound like all the other guitarists. Great rhythm ideas can be found in trying to emulate piano players. Out of the box phrasing ideas can be found in transcribing sax solos.
Case in point, when I was in high school I spent hours and hours (and hours!) transcribing Charlie Parker solos off of LP's. A tedious undertaking of lifting the needle off the vinyl, writing down a note or two and then trying to get the needle back in the groove right before the next phrase. I'm sweating now just thinking about it. I didn't know about the Parker Omnibook, but a book of transcriptions wouldn't have provided the same intense lesson as creating a book of transcriptions.
Writing out sax solos worked my ear and my reading chops and saved me money on the book! I did however get one major thing wrong and that was tempos. I could fathom tempos of 280-320 so I wrote everything at half tempo and thus all the 16th and 32nd notes. See a page below...
I called it "The Parker Tomnibook."
I transcribed piano solos. Synth solos. Jean Luc Ponty and Stephane Grapelli violin solo. Any solo that moved me and made me think, "how did they do that?"
In order to understand how "they did that" it's also important to figure out the harmony, or chord progression. too. That way you can see the relationship between the phrases and the harmony so you can more easily replicate it yourself.