I think it is important to mention to beginners that there are many choices made while playing leads that can make a song sound more happy or more bluesy depending on the feel/mood one is trying to get.
If you stick to the major scale notes you will get a more "happy" sound.
If you flat the 3rd and/or 7th notes in the scale you can get a more bluesy sound. These flatted notes a VERY prevalent in bluegrass, blues, Rock, and old fiddle tunes,
This is done quite often with chords also in rock, bluegrass, and other genres.
Scale example: G Major - g,a,b,c,d,e,f#,G
G with dropped notes = G,A, Bb, C, D, E, F, G
Also: chords are chosen for mood quite often.
The II, III, and VI chords are played either as a major or minor to create a specefic mood/feeling to the experience.
For beginners: I suggest reading some of this and maybe experimenting a bit with things that come to mind, but don't get too hung up or frustrated with it all. It all takes time and much of it comes to one naturally eventually with just spending time on your instrument and listening to music. Take it a step at a time and enjoy the journey.