Keep the scan moving. Technically called “instrument cross-check”, it determines the structure of things, and while you can’t always describe it, you know it when you see it. Scanning the instruments does not mean a random or rushed path, but rather a disciplined approach to assembling all the important information and creating a complete picture of the flight.
The attitude indicator gets the most attention. While different pilots will have different scans, the attitude indicator should be at the centre of all of them. Instruments can fail or lie, but when in doubt, start with attitude. It usually tells the truth.
Have a theory before you make a control input. This is really a mind-set: you don’t “follow the needles”, they follow your plan. Before beginning a take-off, an approach, or a hold, you should have a heading, power setting, and vertical speed in mind – this is your theory. Then, during the manoeuvre, you can look at the instruments with an expectation of what they should show. If reality doesn’t match your theory, make a refinement. This leads to much more precise and stable flying.
Use a few shortcuts. Sometimes you need an educated guess to make your flight a little smoother. Three favourites relate to turns, level-offs, and intercepts:
Know the essential profiles for your airplane. This can make instrument flying a lot easier. Memorize the key power/flap/gear/air-speed configurations for each airplane you fly; including max. climb, initial approach, and final approach. For example, if you know that 20 inches of manifold pressure and 10 degrees of flap will deliver 100 knots in level flight, set that configuration outside the final approach fix and get back to flying. Then, as you approach glide-slope intercept, you can fine tune it if needed. It’s a great way to reduce workload at critical times, and can also bail you out in an emergency.
Remember what matters. Even in a simple Cessna 172 cockpit, there are plenty of gauges, switches, and knobs to distract you. Single pilot IFR is all about focusing on what is important (attitude above all else) and occasionally checking to see how other things are going (engine instruments green? CDI centred? Airspeed where you want it?). If you feel overwhelmed by the radio or an emergency, focus on what is essential and what isn’t.