In order to get this achievement, you need to collect enough gold coins on daily challenges to get the Diamond badge. That requires a total of 25,000 coins. You earn these coins by doing daily challenges.
For most months, you'll need to beat all the daily challenges for about 25 - 27 days to get enough for this achievement. These must all be done in the same month but don't have to be done each day, since you can go back and do any previous days challenge. At the end of the month, the score resets. So make sure you sit down at the end of the month and knock them out.
Since you are doing that many, why not finish out the month (make sure you play the last day of the month to get those last 5 challenges!) and get this one as well:
and since you completed at least one challenge per day, you also can get:
You can find solutions for the hardest challenges for any given day by checking out Voranc on YouTube. https://www.youtube.com/user/Woranc