First, gently and smoothly add elevator back pressure and bring the nose pitch up, using the attitude indicator to guide you. Once you have that pitch set, find your climb airspeed—as long as you continue with smooth adjustments, that airspeed will stay the same throughout the climb.
Simultaneously, add power. If you’ll be climbing for a while, you’ll likely need full power. If climbing only for a couple hundred feet, you may only need a few hundred rpm. Anticipate how the power change will make the nose want to rise, and adjust trim as needed.
In instrument flying, workload reduction whenever you can find it is key. Once you’re established in the climb and you’ve captured your constant airspeed (likely not far off of your typical VY), trim it out and reduce your workload.
Throughout the climb, keep your instrument scan going, and anticipate your target altitude. Then, level off with pitch, power, and trim, and recover to level flight.
In a descent, the first adjustment is power—so reduce your power in level flight, reducing your airspeed to your target descent airspeed while staying level before pitching down.
Reduce your pitch and begin your descent using the attitude indicator to guide you.
Again, time to reduce workload by using our friend the trim. Adjusting the trim may not be necessary for constant-airspeed descents.
Keep that scan going, and as you approach your target altitude, smoothly raise the nose, add power back in, and trim it out. Precision with descents is perhaps even more critical than with climbs, because this skill is what you’ll be using on approaches and what will keep you out of terrain (and away from busting altitudes in real life and on your checkride).