After I have the blocks where I want them on my design wall, I put a pin in the upper left corner of the top block on the left (I always work from left to right). This tells me that this is the first top block of my quilt. Then, starting with the first block with the pin in it, I take & put the block next to it underneath it, then take the third block under the second, then the fourth & put it under the third, etc. until I've stacked up all the blocks on the first row. Take them to the sewing machine & sew the first block (the one with the pin) to the 2nd block (the one underneath the first block & sew them together. Then take the third block & sew it to the 1st & 2nd that are already sewn together, etc. until your first stack of blocks are all sewn together.
To me, the pin is the key. If you drop the block, you still know which direction & position it is. Also, If you drop the whole row after you've sewn it, you know which is the top of the row.
Anyway, this is the method I use.