How can I separate the lid from a can that has a pull-tab/ring without flinging food everywhere?
For most of the removal, leverage rather than brute force will give more control, so you don't accidentally pull the last bit off.
At the end while pulling gently on the ring, rock the lid from side to side, so you're only trying to open one side of the remaining seam.  It's much less likely to flick that way.  While my right hand does that, my left hold the can in such a way that it would probably be in the way of  anything flying, but it rarely needs to.
Another approach is to open the lid most of the way, remove most of the contents, then push the lid inwards to finish breaking it off (or in/out until the metal fatigues and it breaks easily).  This works well for things like beans or custard, that come out easily with a pour/scrape.