My main suggestions are: avoid doing any assisted stretching, and if there's any evidence of swelling in a given area avoid it entirely (or, you can work on it energetically, but: hands off). Those are the two easiest/fastest ways to screw someone up very badly.

It's not that either of those things are inherently bad, but they're things to tread carefully around; even with training, if you're not judicious, you can do damage.

Good Things To Do is such a long list, heavens there's a zillion modalities and minimal training just about anywhere is 500 hours for a reason! But my biggest suggestion is: go slower. Most people start off with an instinct to move much, much too quickly. So breathe in time with the person you're working on, center, and slow down.