The first thing that needs to be discussed is the type of gear that is going to be employed, and by gear I'm referring specifically to the size of rod, reel, and fishing line that you use when fishing for rainbow trout. In my experience the biggest mistake that is made when fishing for rainbow trout in rivers and streams is that the gear that is used is entirely to large. Many years ago I was taught to use an ultralight rod and reel and either two or four pound test fishing line when wading for rainbow trout and this is rule that I still abide by to this day and suggest you abide by as well.
Next we have the way in which you wade in the water that you are fishing. Rainbow trout, especially trout that have been born or survived an extended period of time in the water that you are fishing (rather than being freshly "stocked") are extremely aware of their surroundings and will easily notice anything that's "out of sorts". For this reason you always want to wade mindfully to cause as little commotion as possible when you are wading. Always take slow, steady steps and try disturb the underwater rocks that you are walking on and through as little as possible. Sound travels quite well underwater and if the trout that you are attempting to catch can hear you coming they are much more apt to become "spooked" and thus not bite.
There are many techniques that can be successful when attempting to catch a rainbow trout while wading, but my 'go to' technique has always been drift fishing. Drift fishing is simply the act of allowing your bait or lure to drift naturally with the water as it flows with the current of the river or stream that you are standing in. You can drift fish with a small spinner or spoon and even with live bait such as live worms or minnows, but the point is that if you want to know how to catch a rainbow trout while wading drift fishing is a phenomenal technique to learn.
Wading while fishing is an excellent way to position yourself in the most opportune places within a river or stream to experience success, which is the main reason why wading and fishing for rainbow trout is so poplar. Couple this with the fact that standing in the water that you are fishing and hearing the gurgling sounds of the water as it rushes past and around you, and you've got a recipe for something quite special. The bottom line is that if you add these simple tips to your fishing repertoire and you will not only know exactly how to catch a rainbow trout while wading, you will be able to repeat this achievement anytime that you feel like it.