I often read in various forums that a good upgrade to make on a bike is the wheels. I'd like more information on what to look for in a set of new wheels. What are the measurements I need to understand, how are wheels sized, how do I know if a wheel set will fit a certain bike?

For instance, I have a Trek 920 (2017). It is specced as "Bontrager Duster Elite tubeless ready, 15mm front 142x12 rear." If I were to upgrade this, what specifications do I need to pay attention to? How can I tell if a particular wheel is an upgrade, would fit my bike, is appropriate for my type of riding, etc.?

I'd appreciate any pointers to blogs, websites, etc. that explain wheels, etc.

I think you will find that tires on that particular bike will make more of a difference than the wheels.

Nowadays fast, supple race tires have become so durable and puncture resistant that getting a tire designed for durability and puncture resistance can for many riders be overkill.

I am a big fan of Pirelli and Panaracer Race A and D tires. I have one bike with Continental Gatorskin Hardshells and they do what they say but they are slow and brutal. The added puncture resistance isn’t worth the compromise.

So consider a tire change first.

Learning and understanding different components and standards can be daunting at first. I salute you for asking questions here, I've done it slot myself.

Here's a thread I started in another sub that might be useful:
Help with gravel wheels
https://www.bikeforums.net/cyclocross-gravelbiking-recreational/1201704-help-me-select-new-gravel-wheelset.html#post21488629
​​​​​​Free bump

The wheels on that bike are probably fine. A few years prior to yours (2014), Bontrager had some hubs that couldn't be adjusted and never spun well. If you spin the rear wheel and it stops in 2-3 revolutions, you may have one of those. If it bothers you, then you might look at an upgrade.

Assuming it's fine, get some good tires. I've been very happy with a nice middle of the road offering, 38mm Gravelking SK. Set it up tubeless.

Sure there are lighter tires like the Maxxis Rambler but between durability and ride quality, these are a great balance.

Your wheels are indeed fine. 29'er MTB wheels that are tubeless ready.

To learn about wheels, you must understand how they're built and why. Your wheels have two unique interfaces to the bicycle: the hub axle, and the disc brake rotor. The hub axles are "through axle", which is defined by the axle diameter (yours, 15mm front, 12mm rear) and the fastener type. The disc rotor is generally defined by one dimension, the diameter of the flat disc. Internal to the wheel is the hub to rotor interface, of which there are a few types.

Other things to consider are the rim type, rim width, rim material, tube/tubeless, tire dimensions, tire type. These all matter if you have a particular application in mind.

Want to save weight and improve your ride feel? Give tubeless a try.

So where do you find the information about a particular set of wheels---rim type, rim width, material, etc. Is this imprinted on the rim somewhere?