Sure friend, here's some helpful tips:
1. Read the vocabulary definitions found here:
https://www.head-fi.org/articles/describing-sound-a-glossary.12328/
https://www.head-fi.org/threads/describing-sound-a-glossary.220770/
You don't have to know all of the vocabulary, but start with some of the easier terms to detect (such as veiled, tinny, muddy, splashy, sibilance, etc). Also, note that the list isn't comprehensive, but most terms are there.
2. What you can also do is find posts where people are using the same IEMs that you own, and read what they write. So for example, if you own the KZ ZST or ZS6, there's lots of posts where people talk about the treble being sibilant, having splashy cymbals, etc. Some of the posts even talk about which exact songs they hear the sounds in. Then you can listen to the same songs, and try to hear what they are hearing. When you do, you'll be like "Ahhh, I unerstand what they are talking about now!".
3. As you get better and better at training your ears and identifying the simpler-to-hear terms, you can move on to some of the more technical (and sometimes harder to discern) concepts (such as wide vs deep soundstage, instrument separation, bleeding frequencies, roll-off, etc).
4. Another thing that I found is helpful is to train your ears to certain frequencies. You can do this a number of ways, but one of the best I have found is to install an (iOS) app such as hearEQ. It gives you asy tests that help you to train your ears to hear changes at certain frequencies. What this does is allow you do learn what 500Hz sounds like compared to 1kHz for example. This is helpful for evaluating IEMs, and learning how to describe what the sound is like at different frequencies (such as lower midrange, upper treble, etc).
To do this, you need 3 things:
1). A "calibrated mic" (ranges in price from $20 to tens of thousands of dollars). The cheapest calibrated one that most programs support is the Dayton Audio iMM6 ($20-$25).
2). A coupler to hold the IEM (ranges in price from free to tens of thousands of dollars). Common DIY couplers are just a short piece of silicone tubing, a short piece of vinyl tubing, and cut down 3cc or 5cc syringe.
3). A program to take the measurements (ranges in price from free to tens of thousands of dollars). Some examples are ARTA (free for the PC), REW (free for the PC), AudioTools ($25 for iOS), and Analyzer ($20 for iOS). There are many other apps (including for Android, Mac, etc), but those are the ones I'm familiar with. The apps for iOS are a great way to reuse an old iPhone or iPad. The apps can run on older iOS and don't need cellular connectivity, so an iPhone 4, iPad 2, iPad Mini 1, etc are perfect for the task.
You can even buy an all-in-1 device that combines #1 and #2 above (for example Veritas II
https://diyearphone.com/products/veritas-ii).
A great thread that is very helpful about the measurement topic is here:
https://www.head-fi.org/threads/crinacles-iem-fr-measurement-database-339-iems-measured.830062/
My setup is the Dayton Audio iMM6 microphone, a few DIY couplers I made for free (a silicone tube and also a 3cc syringe), and AudioTools on my iPhone.
Here's a few of the couplers I made:
And here is an example of the type of measurement you get (this is a KZ EDR1 measured with an experimental coupler I made last night):
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(perhaps it is the voice coil or diaphragm). I love the way vocals sound on the ATE, and all instruments sound so accurate (especially acoustic instruments). The stock gel foam tips that come with the ATE are garbage, and need to be thrown in the trash bin as soon as you open the ATE box. I like wide bore tips on the ATE, which take everything good about the ATE and make it even better. If I had any complaints about the ATE, it would be that I wish for a little bit more sub bass, and I wish it had brighter treble (but that is just my personal preference). The shells are very comfortable, but I know some people don't like the "weights" on the cable (they don't bother me though, and do a good job of keeping the cable weighed down).
