I believe that for best fuel economy it is better NOT to use the cruise control. The cruise control obviously keeps you at constant speed whether up hill or down dale. For example, when going downhill, take your foot of the accelerator and coast in gear. If you are showing the MPG on the computer at will show some mad figure like 99mpg because it does not use any fuel whereas the CC will.
Up hill, use as little power as possible to get up the hill and never, ever brake.
For the best ever economy run, watch Jeremy Clarkson drive an Audi A8 4.2 litre V8 diesel from London to Edinburgh and back on one tank.
Sadly, economy driving is, for the most part, very boring, although being a very sad bloke I do try it from time to time. Haven't tried it in the Juke yet, only in my 3 litre automatic diesel BMW and have managed to get about 48mpg from home in North London to Worcestershire. Mind you, I leave everything on including the Climate Control and Ipod player and use the daylight running lights.