I can't tell you how many times I've been listening to a great horn solo, only to be disappointed when the pianist follows that with a monotonous, aimless piano solo full of patterns and run-on sentences. In one sense, it's a little easier to keep a trumpet or sax solo musical; the player has to actually breath at some point. This creates instant phrases, since the musical line rests with each breath. But piano players (and yes, guitarists) can play while breathing so if they're not aware of it, their solos can run on and on and on and on and on and on and on. And on some more.
I've done this too at times. The good news is that this is easy to fix, but does take a little practice.
Here's what I suggest:
Improvise a solo on a tune you like, but don't let your fingers start playing immediately. Let the groove (in your LH or on an accompaniment track) establish itself until you start to "feel" it. Then, and only then, play a phrase. Then wait until another phrase, or beginning of a phrase, pops into your head. Don't play until you actually head a melodic idea in your head. Practicing like this will help you get into the habit of phrasing well playing lines that come from your inner ear, not simply from finger-memory.
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