Know how much per mile it costs to pull your trailer/ 5er or drive your MH.
When choosing a campground or a gas station - know how much it is going to cost you to go 'off course' to get there and back. Sometimes that lower fuel price or cheaper campground really isn't.
Keep your shopping trips to Walmart or the grocery store down to one per week. It is real easy to get in the habit of going to the store every day, and that adds a lot of miles, fuel costs, to a trip total cost.
Work the various loyalty programs for cheaper fuel. We use Costco, Walmart card, grocery store loyalty card discounts, PFJ, etc. Some work better than others.
We buy restaurant gift cards at Kroger when they are on 'sale' with 4x fuel points. That way $100 of restaurant gift cards gets us $400 fuel points - 40 cents per gallon off a fullup.