After your first ten words, have an average word scoring equal or better than 20.
This achievement requires that you get your average word scoring up to 20 points. This is essentially your total number of points divided by your total number of moves taken. The achievement will not unlock until you have played at least 10 words in your Alphajax career. This achievement should be focused on IMMEDIATELY when you start playing the game. If you do not, and you place a bunch of small, low-scoring words, it could take a good bit of time to get your average word scoring back up to 20. In your first game, play the highest scoring words you can with your main account in order to get your average above 20 right away, as soon as you pass the 10 word requirement, and at the very least by the end of the first game. Be aware that passing your turn and swapping tiles counts as 0 points for that turn and will bring down your average. You can check your progress towards this achievement in the Statistics screen from the Main Menu. Look at the "Avg Move" stat.
WARNING: For those of you that played the Windows Phone version, the stats will carry over. If you played a ton of games and words, and have an average word scoring much less than 20, you may have a significant grind to get it up to 20. That is not factored into the estimated time for the Roadmap. We are talking a few additional hours, but in some cases, much, much more. It will depend on your situation. Be warned.