I have always had an estranged relationship with the mustache.
Grow your mustache: beginning moments
When I first started to grow a beard in my early 20's, I went with a chin curtain type of beard - mostly because I had no idea what I was doing, but partly because I always found the mustache irritating and problematic.
When I started getting more of an understanding of what a beard is all about and how to really grow one, I also began to believe in what I now call the "minimum viable mustache".
The minimum viable mustache refers to the minimum amount of mustachiosity a guy should have in order to keep the beard looking balanced.
I will totally and completely recognize that there are plenty of guys out there that have no need for the 'stache - but most of us do.
As for me, it didn't take more than a couple of months for me to realize that if I was going to really grow out the beard, I would have to let the mustache fill in to some degree to balance it out.
Mustache growth over months
For many months, I simply kept it trimmed per the guidelines in How to Grow a Beard and that was enough. Once I started bumping up on about 9 months, I realized I needed to reassess my strategy. I started doing what I used to do with my beard back in the day; I'd just kinda "let it go" for a few weeks, get tired of it, and trim it back.
A turning point for me came when I found the HowtoGrowaMustache.com article about growing a handlebar mustache. It suddenly became clear that growing a mustache is very similar to growing a full beard - It is all about pushing through an initial period of time and molding it into what you want it to be.
Once I read through the article, I knew that I owed it to myself to take a shot at the 6-week training regimen that Douglas Smythe outlines in his article. I also wanted to document this process for my readers.
Without further delay, let's grow a mustache.
The plan, put simply, is to not trim the mustache for six weeks. During this six weeks, I will use a modified version of my Mustache Tranquilizer with a higher proportion of wax for an increased amount of hold, and brush the mustache outward often.
The tools I used for this endeavor are a modified batch of mustache tranquilizer with a slightly higher proportion of wax, and a toothbrush. I found the toothbrush to be an excellent brush for the mustache - but I suggest you buy one to use for this only.

So we begin week zero with a mustache trimmed fairly short. My personal method is to trim the bottom edge of the mustache following along the top edge of the lip, And then put a comb through it at about a 45º angle and trim across.
This leaves the mustache short and out of the way, while at the same time still having some length. This whole thing was fairly simple; just don't trim. The only thing I really had to do in addition to my normal routine was comb the mustache outward - which became quite the habit. During week one, I saw a pretty significant change just from the wax holding it in the shape that it was combed.
The changes didn't stay if I didn't have any wax in the mustache, but the immediate visual of what the mustache would eventually look like was kinda motivating.
At the two and three week marks, you could really see some progress. The mustache was truly filling in, and it was showing. I did notice a need to brush more, but I think it might have to do more with my wax than anything else.
If I had used a harder, more tacky wax, it would have probably needed less attention. I am just not a big fan of those kinds of wax - it is a little too plastic-feeling to me. So, rolling right along, weeks four and five were actually the toughest. More than anything else, I noticed that the hairs I usually keep trimmed were getting longer, and more out of control. They all seemed to be in that

awkward stage of noticeable length and yet not long enough to behave. I a large portion of the mustache began to show a wavy look to it, which was actually many small "pockets" of hairs that would create kinda of a bump - and these would repeat along the bottom edge of the mustache.
A lot of this has to do with shape of the hairs "in training". As it learns to grow a different direction, it is still growing in the original. This means that it will get almost a spiral shape to the existing hair. If I hadn't challenged myself to stick out the whole six weeks, I would have trimmed at this point for sure. But, I didn't.

Once I hit the six week mark, I was pretty happy. I think it was a two-fold change: on the one hand, I did in fact change the way my mustache grows, making it less irritating to keep - and on the other, making myself keep it might have actually changed my comfort level with having a mustache.
I really came to find that the mustache is like it's own little beard - the Beard of the Beard; it has it's own "hazing" stage that also lasts about six weeks. I did actually trim some of the hairs after hitting the six week mark, but not nearly what I was planning on doing.
I trimmed just a few of the strays, and kept the growth going. After about another two weeks or so, the mustache became almost completely comfortable - in the same way it was when I kept it short.
I actually haven't trimmed it since, which makes me believe that it is truly trained. The only times when I do notice the mustache anymore is first thing in the morning and right when I get out of the shower - and a few pushes with just my fingers will pretty much put it back where I want it.

Final thoughts on training and growing a mustache
I struggled with the mustache for a long, long time before taking a shot at taming this beast. I have a feeling that a lot of guys reading this can relate.
Before going through this process, I would have never considered growing out my mustache. If you are on the fence about the mustache, at least check out Douglas Smythe's article and see if it might be right for you.
A good mustache can really compliment your beard, and it doesn't have to be a constant struggle.
Here are some of the products I used. For the most part, I use the products in the Original Mother Lode kit. If you want to try it, use code: BLOG25 for 25% off any of the kits.