Keep a small bank of finished work
At the end of each job, keep one wide photo and one detail photo. Add the location and the job type to your notes. That gives you useful material without asking you to manufacture content from scratch later.
Use three kinds of posts
Rotate between a finished job, a useful detail about how you work, and a simple answer to a common customer question. That mix shows the result, the care behind it, and the experience people are paying for.
Make replying part of the routine
A post is not the whole job. Set aside ten minutes to answer comments and enquiries in the same plain language you use on site. Marketing works best when it sounds like a real person is behind it.