What to Write About...

So I wanted to start a blog but I am not sure what to write my blog about. I see some people have themes and they tend to write about specific things or projects they are working on. I just want to write a bunch of randomness...is that allowed. I wanted this blog to share my really thoughts and events in my life. I want to make sure my family can read it and know what is going on with me. I want my best friend to laugh becasue she knows what the inside joke means. Do I have to have a theme though or can I just write about what I want.