In general there are certain ethical codes that should be followed in order to ensure that the birds are being viewed safely and we aren’t stressing them out. Many birding organizations have their own ethical codes which I will share at the bottom of this page. But overall these are what I have heard from other birders I know and my own ethical code as well.
Respect the birds - Remember you are looking at a wild animal. Don’t do anything that could stress it out or put it in potential danger (ie. repeatedly flushing the bird, distracting the bird from getting food, using its song so it will come closer for more than a few times,stay away from their nests, minimize habitat disruption [for owls don’t shine a light on them for too long]
Don’t do anything illegal - Respect landowners property. Be aware of any regulations where you are birding
Respect everyone in the community - We must remember we are all just trying to appreciate birds, if someone doesn’t know as much as you don’t make them feel bad about it. Be a role model for them try and help them learn a new thing about birds even
Some well known organizations ethical codes
https://www.aba.org/aba-code-of-birding-ethics/
https://www.audubon.org/get-outside/audubons-guide-ethical-bird-photography