It might not be much, but it is the first cabinet I've ever made. Lots and lots of mistakes went into it, making me wonder if two practice cabinet will be enough for me to attempt finish carpentry. The biggest pain was the drawer, followed closely by applying a Polycrylic finish.
The drawer box was made from some scrap 1/2 plywood (outside of the oak exterior, that thing was made from scraps). Warped, delaminating plywood. Since I wanted to be able to just toss heavy tools into it, I made a full floor from the same material - resulting in a warped floor and, thus, a warped drawer box. A warped drawer box won't slide gracefully on its track wheels. Oh no. It will cock a quarter inch to the side and stay that way (reducing to maybe an eight-inch off kilter when loaded). So I put a brick in the drawer and attached the drawer face so that it would be true.
Applying Polycrylic is like trying to paint with water. It cleans up very nicely, but drips and runs were common when using a nice brush. What ended up working better for me was those fifty-cent foam brushes. My routine was 220 grit, wipe clean, apply poly, 320 grit, wipe clean, apply poly, etc. until you had 3-4 coats of poly.
My two pucker moments both involved the door. I practiced with the Forster bit on a piece of scrap plywood, making sure the door would line up. All the hardware was scavenged, and the Blum hinges I used were full-conceal frameless and my box is framed with a one-inch reveal on the sides, so I modified the hinges to work. Anyway, I had the tip punch through on my practice piece, so I was afraid of doing that to my finished door. I'd check every few revolutions with the hinge to see if it was deep enough.
Then, when I got the hinges installed on the door, I attached it to the cabinet box - and it was off by a good quarter inch! I had visions of relocating the hinges and drilling the 35mm holes again, when I remembered that I swapped hinges. Sure enough, there's a side-to-side adjustment screw that, actually, has a wide range. I was able to center the door under the drawer.
Anyway, the best advice I read when making your first couple practice cabinets is to make one, then another. That way, you don't make repeat mistakes and you get to see, twice, how certain issues manifest themselves later (or not).
Now I need to make another, then a table top to span them, creating my workbench.