How to make objects move in a spiral motion?

Just off the top of the head, perhaps set the anchor point to the center of the frame at the beginning of the clip. 

Then move the item well out from the anchor point in the center, and add a position keyframe. Go down the timeline, at the end, moving the center of the object over the center of the frame/anchor point, set another keyframe.

Then add rotation, whatever feels or looks right ... I don't know, maybe 5, 10, 20 times around?

I've not tried this, but think it could work.

Neil