Stretching your freshwater and holding tank capacity is the key to boondocking or whatever term you prefer for camping without services.
How to conserve comes with a number of "it depends" factors such as the size of your tanks, water conservation aids and lifestyle. But, the biggest factor is experience.
As an example, our motorhome has a 105 gal. freshwater tank, a 65 gal. grey waste tank and a 45 gal. black tank. When we first started boondocking with it we got 3-4 days boondocking before we had to dump and refill with fresh water. Now, a few years later, we can go 9-10 days while still enjoying a morning shower each day.
Your RV will be equipped differently but here are a few of the things we've done to stretch the resources we have available.
✓ Our toilet has a water conservation mode, enabled with the flip of a switch. In conservation mode, it causes less water for each flush. When additional water is required, we supplement the flush with water from a 1-gallon pitcher.