To develop proper muscle memory, you need to repeat a task 2500 times. Here is a drill that can be done literally "at ease" and at pretty much zero cost.
This is some of the "homework" that I give my students:
You will need the following:
1) an EMPTY weapon
2) several EMPTY magazines (for that gun)
3) a towel of sufficient size to cover your lap
4) a comfortable place to sit.....preferably with your feet up.
With the towel covering your lap, dump all the mags onto the towel.....yes dump, you want the mags all jumbled around.
Now, with the EMPTY weapon in your strong hand, use your support hand to locate any one of the mags on your lap, orient it into the proper position (bullet side should face your index finger) and insert it into the mag-well, seating it as if you were loading the gun. Feel free to watch yourself doing each step.
Go no faster than is needed to do each step correctly.
Next, using the mag release, drop that mag back onto your towel and find another mag, locate, orient, insert. Keep repeating the process until you can do it without looking.....then keep doing it. The object here is to do this without looking or even paying much attention. Watch TV, carry on a conversation, etc. but keep practicing.
Wanna step up your game and give your sense of touch a little bit more of a workout? When you can do this drill properly 50 times in a row, replace the towel with a paper sack or a small box. Now your doing the drill without even having peripheral vision to help you out.
But your not done yet. This drill simply trains you hands to identify the magazine and properly orient it for loading.
The next step is for you to decide where and how you will be carrying your extra mag(s) and then practice taking them from that chosen location and getting them into your gun. Very similar to the aforementioned drill, but necessarily more involved due to the location of the carrier and holster you choose.
One thing to remember, it is not practice that makes perfect......it's perfect practice that makes perfect......don't fudge on any of this.
Go slow at first. Speed will come with practice.
With enough repetitions you will be able to do this in the dark with a bear chasing you during a hurricane............ 8)
Here's what "being one with your equipment" looks like:
https://youtu.be/Hgdq1FBYTUE