This is an achievement that requires some skill and lots of patience.
Try and get as many square on drops, don't worry about combos or your population total. Try and focus on the bottom corner of the dropping block and get it in line with the matching corner below. Take your time and if you have to wait for it to swing back round.
If you drop to many blocks off center the tower will sway to much and the blocks dropping won't "stick" as much to the tower so try your best to get them square.
There is no easy way to get this i suggest getting up and walking away for a bit every hundred blocks unless you on some kind of a roll.