Just do it. Don’t agonize about whether or not it’s any good just DO it. Pickup your guitar, start noodling. If you find yourself falling into familiar licks, stop. Redirect yourself. My wife hollered down to my just the other day; “What was that? I liked that.” I told her I didn’t know what it was I was just playing something that sounded pleasing to me. I was droning on the A string with my thumb and picking a melody on the top three strings. Is it a song? Nope. But it’s the germ of an idea. You can’t write Hey Jude right out of the blocks. But you can’t write ANYTHING if you don’t try.