Teachers often tell me they don't know what to post on their grade level blogs.
I think that anything that students would be excited to share is great content.
You can also post links to other teachers' blogs or take excerpts from Ann's Principal newsletter or from the PTO's emails.
If you are producing a paper newsletter or other document that goes home, it's helpful to also post this information on your blog. You can divide up each topic in your newsletter as a separate post and schedule them to go out automatically over the course of the week or month.
It always helps to have an image but this is sometimes hard if all children haven't returned photo permission forms. There are many other things you can use. You could show work being done in class, pictures from field trips, shots of guest speakers, or photos of books students are discussing.
Several teachers post pictures of students working on something together with the children just out of the frame. See some of the other grade level blogs for ideas. I'm also happy to brainstorm with you.
Any news from your class gives parents something to ask about beyond the usual "How was your day?" and that is always appreciated!