As the description states, this achievement pops when you hit or exceed a 12 chain. While normally this is purely left to chance, you can weigh the odds in your favor.
1) Start a run on your favorite rank.
2) Play until you fill your inventory with one "Wood to Key" or "Stone to Key" scroll and 2 (3 if upgraded) keys. The reason to use key scrolls is that you don't normally spend key pieces regularly, so using key pieces for this will not impact your ability to progress as much as weapon or staff pieces.
3) Die
4) Start a run on Rookie rank.
5) Play, but focus on keeping keys and your scroll's conversion resource on the board. The keys you picked up will help with this by letting you breeze through a few chests/doors.
6) Once you're satisfied with your board, use the scroll. Not only will you start with a few matches, the sheer amount of removal will clean the board, increasing the chance for more cascade matches.
7) If you got 12 or more chain, hooray achievement! If not, die and repeat.