deciding on a melody

its not too hard to decide on a bassline but for a given bassline there's so many different melodies and when im trying to write, i cant decide on one.

what's the most natural way to songwrite?

i'm just lost. i;'ve been avoiding songwriting lately and just have been working on playing different classic rock riffs thinking that's gonna get me somewhere.

i wanna go back to the basics. any ideas?