Misc Objectives are the menial sidequests that are not developed enough to have a quest-name for themselves. They can be acquired by overhearing conversations/being talked to, reading notes, or simply talking to people. These objectives will show up under the "Miscellaneous" section of the quest section in the pause menu.
Tip: Talking to Adrianne Avenicci in Whiterun ((she is the town smithy, thanks to Kaiser679 for the correction :], should be found outside Warmaidens, right by the main entrance to Whiterun)) will give you 10 consecutive misc objectives that can be done in around 2 minutes, this could help take the grind off this achievement partially.
I will update if and when I find more easy/quick objectives, feel free to comment if you find some i'm unaware of.