Fair use and leaving things how you found them are the main themes. It is customary to empty the receiving flask into the waste container after use. The seals at the recieving flask and the gas release tap should be wiped clean and coated with Dow Corning high vacuum grease. If for some reason you used any other type of grease it should all be removed thoroughly using an appropriate solvent (hexane and ethyl acetate). If you used Dow Corning high vacuum grease on the join between flask and vacuum tube to achieve very low vacuum even this must be washed off from here when you are finished as the default condition for this join should be ungreased.
You don't have to use a splash guard if you are confident without one. However if you do use a splash guard, this does not excuse you from cleaning the vacuum tube with acetone after each use. Just because your mixture didn't bump, some of your compound may still have entered the vapour phase enough to land on the inner walls of the tube which can drip down into the next user's flask (If you can smell it, it's there). Apart from removing the vacuum tube for cleaning which should always be done, there are a few other ways to improve this cleaning, such as filling a beaker with acetone and sucking it straight up into the tube with no flask there, or filling a flask with a solvent and simply rotavapping clean solvent through to wash everything into the receiving flask.
If you are in a lab where two or three rotavaps are linked to the one pump, communication is the key at the start. Tell the person next to you what solvent you are removing and they ought to reciprocate by telling you the same. If you walk away, leave a note with your name and the solvent being removed. You can write this note on the glass part of the rotavap with a Sharpie.
A common scenario is a novice removing water who decides to speed up their process by occupying both rotavaps at once for several hours at the exclusion of others. If you want to use more than one rotavap at a time it should be brief and well communicated - or done at night time when not many people are around.
Another problem is somebody who alters the settings on somebody else's flask when they are not around. This is not only rude but potentially mayhem is a precious mixture is bumped. Don't touch somebody else's rotavap unless they asked you to or unless you see that there is clearly a hazard.
When you are done cleaning the rotavap, leave the water bath on 40 °C unless it is the end of the day when it can be switched off, as well as the chiller.