So, the first thing I'll say about the achievements of this game is that they are extremely straightforward. If you go through every part of this game you will get every achievement barring 1. If you look at the achievements you will understand where to get every achievement barring 1. That makes for 2 potential missing achievements.

And you know what? That's enough for me to have wished there had been a guide out there. So I wrote one!

(Disclaimer: I have not gotten all of these achievements myself yet.)

For the sake of completion, I'll briefly list the regular achievements. I'll use the term 'variant' to refer to the vanilla variant, the standard 14 variants, the (currently 9) hidden bonus variants, and finally the UW variant, which appears to be the only combo variant with achievements linked to it. I'll use 'combination modes' to refer to [+] and [#].

• Complete [x] levels in [variant]
  There is one of these for every variant that asks for 5 levels. The two combination modes ask for 10 levels instead.
  
  
• Perfect 10 levels in [variant]8x8
  There is one of these for every variant, as well as the two combination modes.
  
  
• Unlock [x] gallery
  There are 4 of these, one for unlocking each of the grid sizes.
  
  
• Perfect the [x] gallery (excluding bonus variants)
  There are 4 of these as well, one for each grid size.
  
  
• Master of minesweeper variants
  Perfect 10 levels in [+][#]8x8
  
  
• Grandmaster of minesweeper variants
  Perfect 10 levels in [+][#]8x8!

There are only 2 achievements that fall outside of the standard achievement formula and had me scour the forums to find an answer.

• All Directions: Use a hint with both horizontal and vertical arrows in [B]!
  This is actually straighforward as well, when you realize that the ! is part of the variant name. If you're anything like me you've looked at this achievement way too soon, before ever encountering the harder variants. The very first puzzle of the B!5 variant had this hint for me.
  
  
• Blank: Find a board with no starting clues
  While the least straighforward of all, this one is actually surprisingly easy to find! The first puzzle of OT7 appears to always be a blank.

• Tab 1
  - Perfect 10 levels of every variant in every size
  
  
• Tab 2
  - Activate hint when you open the first [B]!5
  - Perfect 5 levels of every variant (can do this with only 5x5!)
  - Perfect 10 levels of [+] and [#] (can be done with only 5x5!)
  - Unlock and perfect 10 levels of [+][#] 8x8
  
  
• Tab 3
  - Perfect 3 levels of OT5 and 6
  - Perfect 5 levels of LM, MX, MN, and NX5
  - Look at the first level of OT7
  - Perfect 10 levels of UW8
  
  
• Tab 4
  - Perfect 3 levels of every variant to unlock size 8x8
  - Perfect 10 levels of every variant's 8x8
  
  
• Galleries 5-8
  - Perfect 1 of each standard combination (rows Q-B, columns M-E and #)

NOTE: The gallery achievements also require you to have perfected 10 levels of each standard variant. This is why tab 1 requires perfect completion of the entire tab, rather than just size 8x8 as in tab 4.

And that's it!

No wonder there was no guide for this before, I did not expect this to be as short as it is, but alas. As an achievement hunter I'd hoped for a guide like this to be out there, but there wasn't yet, so I decided I'd create one on the odd chance that someone else was also looking for this information.

I hope this helped someone out, and let me know if anything is missing!