hey i dont know too much about music theory, but i have the major scale down. the problem is when i just mess around with it the scale sounds pretty crappy. when i mess around with a pentatonic scale it sounds fine, but i dont know any advice would be appreciated like certain notes to be careful about playing or certain notes to play with certain backing chords. Thanks.
VERY good question to ask. It is often said that creating a b9 interval with any note in the chord is tense and somewhat dissonant. For example(all in C Major), playing an F over an Em, Am, or C chord(F over the E in each chord). The generally "safest" notes to solo with are chord tones, but again, the b9 thing is still there. A C over a Cmaj7 creates a b9 with the B and might still sound a bit tense. The pentatonic scale is essentially the major scale with the tension notes removed(fourth and 7th).

I'd just like to say, when I say tense and dissonant, that doesn't mean bad.Sometimes, you DO want tension, maybe playing an F over an E7 chord in an E7 Am cadence.
I Use a lot of slides, hammers-on, and pull-offs to diminish the "happiness" of that scale.
Make sure you're in the right key, be aware of the chord changes and make sure you listen to what you're playing.

As far as notes go playing around with the root, 3rd, 4th and 5th can give you a nice melodic hook, the 7th and 2nd are good for when you want to lead back to the root and anything inbetween is good as passing tones to add interest, tension and dissonance.
Actually called Mark!

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