Being a fan of karaoke I'm sure that you've been to shows hosted by various karaoke KJ's. You've noticed that every KJ has his/her own style of running the show. You will also need to develop your own personal style. Beyond this there are some basics that we'll discuss here.
You should go to the establishment sometime during the day to set up your equipment and make a sound check. Now at show time you will only need to turn everything on and pass out song books. It's never a good idea to go in an hour before the show where you have to carry in your gear past a crowd of drinking people.
If this is a place that you have never performed at before you may want come in a little early to mingle with the customers some to get a general idea of what the crowd is like. You may also be able to talk a few people into signing up to sing before the show even starts. This can be a big help if you look out at the beginning of the show and nobody is even looking at the song books.
How you announce yourself and start the show is all up to your personal style. You should however include an announcement on where the request forms and pencils are located as well as the procedure for signing up to sing. Keep an eye out for anyone that may seem confused or appears to need your assistance.
One thing I really dislike is when a KJ thinks that his/her job is to entertain the crowd with their singing and entertainment skills. The KJ's real job is to help the crowd entertain themselves. Never use your shows as an opportunity to show off. You will regret this when people stop showing up.
Breaking your rules of singer rotation is one of the biggest mistakes you can make. People remember where their place is in the line up and they will resent you if they believe you are playing favorites. This is to say, for example, that they notice the same person sing twice since their last time up. This brings up a slight problem. What if 90% of your singers are only singing slow, boring songs and it looks like much of the crowd is ready to fall asleep or leave? I solve this dilemma with DJ dance music. "Hey guy's, we're gonna take a little break from karaoke to play a few dance tunes." This has always worked out well for me.
No matter how fair your rules of singer rotation are you are still going to hear complaints from some customers that believe they didn't get to sing enough. Usually you can just shrug these individuals off and go on about your business. Sometimes however, you will run into someone that simply becomes a nuisance and disrupts the show. This is the time to inform the management as opposed to dealing with this person yourself.
This is something I've seen too often. A KJ is doing a 10 pm to 2 am show and at five minutes till 2 he announces that "this is the last song of the night" (which he sings) and then shuts down right at 2 am on the dot. Very often at this time of the night there are maybe only two or three singers left that have been there most of the evening. If they only have one or two song requests left, and the establishment doesn't mind, it will not hurt you to stay another fifteen or twenty minutes to let them sing. This is always appreciated and helps you build a loyal following.