Good words Daniel!
I know I complain about karaoke sometimes, but mostly it's lots of fun! Just be yourself, and have a great time.
Oh, just remember, that you may get good singers, but also a few bad ones! - treat everyone the same! They all deserve their applause for getting up to sing in the first place. Treat them as if they're all brilliant, even if they aren't!
One good piece of advice - be fair. Don't let anyone 'gatecrash' the karaoke - I always keep it strictly in the order in which I receive the requests. Quite often you'll get someone who has had a few drinks too many, trying to be the next singer. Don't let them do that, as it upsets the people who have been waiting their turn.
Lastly, don't worry too much about the background music - I usually put a playlist together and let it autoplay - you can always fit a certain song or two in the list if you get requests for non-karaoke songs.
Just one more thing - if someone is so bad that you need to laugh - run and hide somewhere! I had a singer once who was just about the worst ever, and the audience was laughing - so I couldn't help myself! The person threw the microphone at me and stormed out of the bar! Of course, this set the audience off even more!
Best of luck - have a great night, and let us know how it goes.
