If you tap out the rhythm of your melody line on the tabletop, does it sound interesting without the help of the words and the pitches? Would anyone have a chance of recognizing your song just from the rhythm of the melody?
It's okay if the answer is no. There are many good, successful rock songs with nothing interesting or distinctive in their melodic rhythm. But if you want your song to be catchy and memorable, to get listeners' attention and to stick in their memories, then take some time to look for ways to make the melody's rhythm more distinctive and interesting — especially in the song's chorus and in the hook line.
When I set out to write music for a finished set of lyrics, I write the rhythm first. I don't start thinking about notes until I've settled on a tempo and feel and sketched out the melodic rhythm.
Often, at this stage of writing, I make some edits to the lyrics so that the words fit neatly into the rhythm scheme. Sometimes I have to rephrase things to add or remove a few syllables. I make sure that each strongly accented note lines up with a strong word, a word that deserved to be emphasized.
I've learned from experience that if I don't get the right rhythm to start with, I'll end up at a dead end and have to start over anyway. And if I do get the rhythm right, the notes fall into place without any great effort.