Gary's advice is well taken -- in that it is a good idea to start looking at not much less than half a tank. When my needle is on half a tank, I have used more than half, but that is when I begin finding a station that will work for my rig with toad (34' foot Class A plus Jeep Cherokee). And also, as he mentions, try to avoid the stations with pump islands perpendicular to the station building unless one on the end will work for you.
For me, the reason to begin looking early is the cost of fuel these days. You may find a great station for in and out, but the price is sky high - and if you are getting low will have to use it anyway. Each time that happened to me, invariably, 5 miles down the road I would find another station that would work and gas would be much cheaper than what was then in my tank.
As you travel more and more, you may be taking some of the same routes and will remember where a station is that worked and also had the best prices. Each year that I travel from NCal to Quartzsite, I know exactly where I am going to refuel along the way -- including my last stop to fill before boondocking on the desert. It is in Parker, 23 miles from my destination, easy in and out, and a price for both gas and propane that has always been cheaper than any station in QZ.