Oh, I think that's an easy one. Most of us putter around with our arms in the tank all the time. Most of the time my fish rather like the entertainment, they usually seem to have fun with it. Don't move things around quickly - it's just the opposite - take your time and always be sure nothing is going to hurt a fish. It is unfortunately easier than you might think to scratch or crush a fish, both with purly decorative items like rocks but also with filters, heaters and such.
Gravel cleanings and moving things around can indeed kick up debris but overall it is nearly always less stressful to just stay in their familiar environment. There are exceptions of course, like major removal and replacement of the substrate perhaps.
Oh, and another thing. People talk and worry about the "stress" of water changes and tank work but most often those actually pale in comparison to the stress of toxins in the water. When a fishkeeper neglects to do good water changes, the resulting debris breakdown may result in blips of ammonia and nitrite that are not good for fish. So never feel bad about rolling up your sleeves and incorporating a good water change into the other activities that make your tank look good.
And remember, do whatever it takes to ensure that you won't forget the basics of a good water change. As a beginner you should always get in the habit of using a good water conditioner and of roughly temperature matching the return water. Prime is our most highly recommended water conditioner and I'd recommend a dosing of 1.5x to 2x what the instructions say (this is because water authorities sometimes "shock" or overdose the chlorine products.) If your tank is 6 months old or younger then be careful to not exceed 2x overdosing on the conditioner as this can slow N-Bac growth (which is still going on at 6 months out of course.) Rough temperature matching can be done by simply putting your hand back and forth a few times between a cup of tank water and the tap water you are adjusting the temperature on (I simply us a mixing tap and mix hot and cold household water but I know that I have a fiberglass lined hot water heater, so excess metal content is not a problem from our hot water and in the vast majority of cases is not a problem for most people.)
~~waterdrop~~
