Simulator time, simulator time, simulator time, simulator time.
Simulate the leans in a non-motion sim by getting the instructor to replace one of forward views with one of the side front views with a downwards offset angle. Nothing out the front window makes any sense to your brain and the instruments become your best friend in the world.
No, I haven't tried this in real life, but after many hours of practice I have completed several hour-long IMC cross-country flights in the simulator with map reading, nav radio operation, etc, both in daytime and full black night settings, with wind buffeting, lightning and rain.
Note that I am not saying I would presume to be better than an ab initio pilot with no experience at all if I was flying a real aircraft, the point is this: it took me a good 10-12 hours of practice in instrument flying to be able to do that in the simulator (on top of the hundred or so hours of VFR sim time), and I pity any non-instrument-rated pilot who finds themselves inadvertently in IMC.
Even an EMS pilot I've spoken to lamented the lack of preparedness for black night bad weather operations, as have several Army pilots.