If you have words already, then start by editing them to make sure that each verse will fit into the same number of beats... this doesn't have to be absolute, as you have some flexibility in how you fit words in, but that would help... such as: If you had verse one starting with-
The orange sky bright behind the dark grey clouds (space)
1 2 3 4 5 6 7 8
then try to kinda match that 8 beat first line structure with each verse... this isn't a rule, but when you are starting out, it helps to create a structure that feels consistent.
If you DON'T have words yet, then make up a verse and chorus pattern first that you can comfortably play and remember, then write the words to fit your structure. I like the suggestion Neal made, too, about finding something else you like and adapting it.... just make sure that you change it enough that it has a life of it's own, and doesn't just sound like "Susie Q" with one chord changed or something.
Good luck, and if you get stuck, post part of what you've got and where you're stuck.
