first just pick a key you want to sing in .
after that play around with the chords in that key for example:
say you want to play in Cmajor it might go like
C F C G Dm F Am G
that would make a nice verse progression
then do something simple for your chorus like
C F C F C Am F
Then do something for an interlude
start by just playing around with the Cmajor and Cmajor pentatonic scales and add a few bends and accidentals
Heres the two scales:
major
---------------------------7-8-
-----------------------8-10----
-----------------7-9-10--------
-----------7-9-10--------------
-----7-8-10--------------------
-8-10--------------------------
major pentatonic
------------------------8-10---
-------------------8-10---------
---------------7-9--------------
-----------7-10-----------------
------7-10----------------------
-8-10---------------------------