Congrats on the new rig. As others have said, they can all be a bit different. You will just need to go for a test drive and get a 'feel' for what your coach does.
In general, my way of doing this, with a 2 stage Jake:
-I usually leave it off in normal highway riding, as Wolfe says on RV.Net, it's that coasting that gives me my best MPG
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-When in city highway traffic, I use low stage, to help me in stop and go traffic. I also set our US Gear Toad to a 7 position, in case of emergency stops.
-On rolling down hills LT 6%, where 55mph is safe. I use the brakes to slow down to 55, then kick in the low stage.
-On GT 6%, or in twisty 45MPH or less speeds, I slow down to 45-50MPH, as appropriate, then engage high stage. Also using the service brakes as needed, if slower curves or speed builds up.
-Our Country Coach, ISL, currently has high go to 4th gear. As needed, I'll down shift lower. (As mentioned, watch your speed in relation to the gear you choose. Most times the computer between engine and trans, will not let you hurt them. But, I try to be sure the gear and speed keeps the RPM below the top end.)
-Also check you rig on Cruise Control with Jake. Our Jake will not engage, while in Cruise Control.
-When in doubt, go slower then you think is needed, until you get a real good feel for your trans/jake low & high/service brake combination.
-When I know I have heavy mountains up/down on a course. I keep the fuel planning a tanks of water/grey/black as low as I feel I can. (If boondocking, and no place to fill water, makes a difference. But when on the road, and hitting parks most nights, we travel with about 1/4 -1/3 water.) Each rig's fuel tanks and MPG is different, but with ours, I'll try to plan a 1/3-2/3 fuel tank or less, depending upon distance to be traveled the for that day. (This is all after learning your rig, and I never take a chance of dropping below 1/4 during a trip. I also get my fuel level to where I want it Full (or less if mountain driving) at the end of my day travel. Ready to head out in the AM.
Relax, enjoy learning all the new things in your rig, have fun,
Smitty