This might be a bit of a pain. But if you're like me, remembering which settler is assigned to which tasks gets overwhelming after a while. I was trying to figure out how I could keep track of their assignments and thought of this...
1) Keep cheap armor pieces and rename them at the armorer's workshop to something that reminds you of a new task you are about to assign. Then just give that piece of armor to the settler you assign the task to. In the future, you can trade with them and read what you've already assigned in the past. It has the double advantage of equipping your settlers with armor in case of attack. Also note that the use made names can be quite long, so you can reference more than one task in one piece of armor if your nomenclature is concise.
2) You can even reference the settler's bed assignment. Place varied furniture outside of each shack you make and/or use varied colored doors and reference these in the name of the armor you make. Add the location of the bed, like floor number, right, left, center, etc. For example, I put a chair and a red door in front of one of my shacks and had a settler sleeping on the second floor on the right side, so the armor was called, "Bed CR2Right" for Bed, Chair, Red door, 2nd floor, right side.
3) I've found that keeping farmers far apart helps with assignments. I grow one crop in one area and assign one settler (it appears Beth did it this way in the game as well). It seems that additional crops get auto assigned to workers, even if you attempt to manually assign them. Having two workers in the same farming area sometimes creates conflicts when adding new crops. I've seen this lead to certain corps becoming unselectable - in regular and workshop mode.
Got any better ideas? Tell me...