listen to the main melodic flow of the verse you have written - hum it, simplify whatever it is to the point where you can easily hum it sing-songy, almost like a nursery rhyme. then see if you can get some simple melody from it that seems compatible. from there, it's just a process of careful building.
another thing to try is take the melodic and rhythmic structure of the verse and compare them to the lyrics. then take the lyrical concepts going on in the chorus or bridge and see how they differ from the lyrics in the verse, and try to change the music in the same way. if the lyrics get darker or more intense in the chorus than in the verse, then make the music so also.
the best way to do this is to listen to songs you like and see how the songwriters handled changes. try to understand the concepts behind what they were doing. try to find familiar patterns in different songs by different authors.
and most of all, experiment, make _something_ and then listen to it and see how it is lacking.