I look at part of my job as keeping the stars of our shots safe from whatever it is I'm doing to achieve them. We use a lot of heavy stuff with sharp corners and also create a lot of trip hazards. I once worked with a DP who refused to allow me to ever lay a dance floor in such a way that an actor could step on or walk on it. This included just laying the room so that they were always on it. I had to make strange cuts and customize each floor which took forever when I could have just laid a pad and kept them on it the whole time.While this is a little extreme, I do try to minimize anything that may possibly break their concentration or cause a hazard while they are trying to do their thing. I'm always looking for anything that I may have done that might injure them. I'll put a tapeball or a duventine pad on sharp dance floor corners or, if they must somehow cross a piece of floor and aren't wearing shoes, I'll make a pad of duventine across the edge so if they do catch it, they won't stub their toe. I always, if there is an opportunity, point out any trip hazards to them. If possible use floor, planks or an offset so they don't have to cross track.
My least favorite shot to do is a camera looking straight down on an actor. This one always gives me the willies and I'm always relieved when we get it and move on. You should never have a camera over anyone without a safety. I usually screw a bolt into the plate to stop any danger of the camera sliding off and will attach a daisy chain safety from the camera to the dolly, or run a line to the grid overhead, or even build a goalpost with speedrail over the camera and run a line to that. In addition, if it's a static shot, I'll take out the boom control handle and build up under the arm with apple boxes or a small combo stand. Leave nothing to chance. I've even had actors ask me if the camera is safe and I'll take them through all the precautions we've taken. Incidentally, all this should be done with the stand-ins also. Don't let yourself get bullied into shortcuts by a DP in a hurry or an AD who's trying to stay on schedule. Usually you'll see this shot coming and will be able to have the stuff waiting in the wings to be used. Always be looking for what could go wrong because if it can, it will and your career and more importantly, someone's safety and even life is on the line. If that little voice is speaking to you from the back of your head listen to it.
Anyway, just a couple of things to keep in mind.