Standard way for novice to prevent small round plug from rolling away while soldering wires to it

Figure 1. Image source: iFixit.

This works well for me. Increased grip is possible by increasing the number of "wraps".

There are many ways to fix things during soldering.

One popular method is to use so called helping hands

A wooden clothes peg (clothes pin in American English) works very well:

it won't suffer from solder drops or brief touches with the iron, and has more friction than many other sprung solutions so is less likely to ping at the wrong moment. You can always rest a book on the handle end to add more weight. If you're equipping a classroom, they cost next to nothing.

I used to keep a couple with my portable iron in a travelling toolkit; the soldering parts of that were mainly for cables/connectors.