I didn't know for sure where IO was going either when I started and worried the same thing as you. I had about 10 things I knew I wanted to blog about at the beginning.
I made a point to update twice a week, and am pretty good about it. Sometimes I'll have a day where I can think of five things to write about, sometimes I sit in front of my computer screen trying to write a post due that day and absolutely nothing comes to mind. It does take some effort to push through those "dry" spells and not give up on the whole thing - especially at the beginning. Once you do it regularly for several months it becomes a habit and is easier.
My posts are generally about three different things: Travelogues - which are accounts of the places I go, the parks I stay in, the destinations I visit. They are personal to me - "Today I went <here> and did <this>".
RVing How-To - which are posts about my RV, the RVing lifestyle, and full-timing. These are designed to help my readers out who are looking to go RVing themselves.
Philosophy - My thoughts on life that pertain to RVing and travel. Like minimalism, valuing experiences, inspirational posts, traveling before retirement, goal setting, etc.
Then occasionally I'll think of other things that my readers might find interesting. Like a blog post about photography, since a lot of people who travel like to take pictures too, or exercising while traveling, etc.
Hope this helps!