Karaoke club work!
When you do a Karaoke show in a pub or club you'll often be torn between your audience and the club owner. Owners often want dance music to be played so there are more drink sales and often the only reason patrons are there is to SING! So how do you find a happy medium?

The owner's motivation is to get more alcohol sales AND do Karaoke. Your motivation is to keep the owner and the patrons happy so you get paid! Many entertainers solve this problem by scheduling four or five very intense dance sets interspersed through at least one or two full rotations of Karaoke singers. You could lead this in after your last singer at the bottom of your rotation and then slam on the Electric Slide, and follow on with some fast dance music (at least 120bpm) for your first set. The 2nd set you could put on the Macarena, and follow on the same way. Use the most popular dance tunes to pack your floor, then make them sweat. Get them real thirsty so they crowd the bar and order more drinks, making everyone happy!

Here's a tip to pass on to your club owners. Ask them to put out free Tortilla Chips and salsa. Keep it going all night long, and as the night progresses, people will order more drinks, increasing the sales. Do those intense dance sets, and the combination of dry Tortilla chips and fast dance music WILL produce more sales.

Karaoke Games:
Announce that you have a tune loaded up, and the first singer that can answer your trivia question and bring you the right answer written on a napkin gets to sing the song. You announce that these tunes do NOT count against a singer's regular rotation position. So if Fred is signed up to sing a song right after these tunes, and he wins the trivia contest, he will sing twice in a space of 5-10 minutes. Of course, you load up a really silly song that is either hard to do, like "Beat It", or load up a very well known song that someone can vamp to such as "Like a Virgin"…. Do two or three of these in a row, get the singers up, then go back to the regular rotation.

Wrong gender duets:
This is exactly like it sounds. Get the club to put up (or buy yourself) a six pack of beer in an iced bucket. Announce to the crowd exactly what you want…which is two volunteers to sing an unidentified song that is the wrong gender. (I.E. two guys sing "Does He Love You", or two girls sing a Righteous Brothers tune). Give them the big warm up announcement, play the tune, and let the fun begin. Occasionally, you will get two singers that will really nail a tune and they will get a huge ovation.

Novelty songs:
Announce to the audience that you need several guys and girls to sing Love Shack. This wonderfully tacky tune attracts the mid 30's crowd like no other tune. Go to other shows in your area to pick up tunes that really seem to get the crowd going, and are group participation songs, and use these in your shows as novelty tunes.

Contests:
There are pros and cons to doing this and it pays to consider the implications:

Pros -
Increased attendance
The opportunity to hold a contest on a night where you might normally not play (Money)
Promote your show
Increased exposure
Less of the "when do I get to sing" question from the audience
Much easier show to "run"

Cons -
Figuring out the fairest way to judge the singers (picking a true winner)
Getting qualified judges who are impartial
Providing or arranging adequate prizes to attract participants
Dealing with disgruntled or angry performers who did not win

Other ideas:
Limbo contest
Conga line (watch your night club owner have a STROKE as you tell the line to LEAVE the restaurant or bar and go outside, then come back in)
Hokey Pokey - As corny as it sounds, this does work, although you will need to read the crowd first.
Pass the hula hoop
YMCA

Spice up your existing Karaoke show. Remember to do two things:

1. Never do the same thing week after week. Repetition is boring. Keep it lively!
2. When you sing, as the Karaoke host, give it everything you've got. If you can't sing, or don't want to sing, cultivate relationships with "regulars", spotlight a different regular each week, introduce them, and let them do the singing for you.