Have them call you by your first name. This sends the signal that you're one of them. If they try to call you "Mr. So and So", insist that they call you "Dave" or "Chuck" or "Bob". If you have an unhip first name that does not lend itself easily to contraction such as "Everett" or "Mason" or "Virgil", make up a nickname for yourself that is more suitable. This is easier in the south, where you can get away with people calling you "Skeeter," or "Chigger" or "Hoss." Depending on where you live, "Possum" or "Catfish" might also do. This will implicitly tell them that you are no better than they are and will eliminate the impression that they have something greater to aspire to.
Wear sneakers. Sandals or thongs are even better. Oh, and wear shorts. Even in winter. This tells your kids that they needn't take things too seriously. Seriousness implies challenge and sacrifice which may have been good for males in more masculine times, but for today's more effeminate male is unbecoming. Besides, seriousness isn't fun. If your youth group is co-ed, the girls will already be wearing shorts, flip flops, and skimpy tanktops. Be careful: this could counteract the feminizing effect of the rest of what you do.
Have pizza. Frequently. Pizza sends the signal that you are informal. It's easily acquired, you eat it with your hands, and all you have to do to clean up is to throw away the box. Pizza is to formality what a cross is to a vampire: it drives it away sqealing. And if it is accompanied by drinks served from 2-liters in plastic cups it is guaranteed to keep formality at bay.
Play games. Not only are games fun, but they take up time that would you would otherwise be expected to use for studying something substantial, like the Bible. Studying the Bible takes time and effort and requires actual thinking from your youth. If you find yourself in a position where you have to do it, make a game of it. Effort in any form in which it may be recognized as such should be avoided at all costs. You also will want to use a modern paraphrase when you do read the Scriptures--or at least a Bible with an appealing title like "The Adventure Bible" or "The Teen Bible." Don't ever let your youth get the impression that they will have to put forth serious effort forth in learning about the Faith.
Stay topical. If there is time after eating and playing to discuss anything substantive, make sure you stick to relevant topics that the kids are already familiar with. This will help keep them focused on themselves and their own concerns. If you try to take them beyond where they already are, it will come of as too much like school where they are expected to actually learn something. Self-discipline and hard work may be fine at school, but remember, this is religion we're talking about here.
Give them something colorful to write on and tiny little pencils to do it with. This will keep the mood light and breezy. Colorful, cartoonish worksheets are ideal. They can be filled out easily and thrown away quickly--preferably on the way out the door. Make sure your kids don't have to take anything home with them: this might give them the impression that what they do in youth group has implications outside Wednesday night.
Watch movies. Not only does this get you out of doing something you would have to mentally prepare for, but it keeps the focus on entertainment. You have two options here. You can show something religious, as long as it is cartoonish and silly. Veggy Tales are perfect: they give you the impression you did something religious even though you really didn't. Alternatively, you can show a popular secular film and pretend it has religious themes. After the movie, you can spend five minutes discussing them in a cursory way before everyone gets antsy and wants to go home anyway.
Do your own thing. Keep your kids in their own age group and try to stay away from older members of the congregation. These are people who do uncool things like work and support their families. Exposure to senior citizens should definitely be avoided. They come from a generation in which children were not expected to be entertained all the time, and they might remind your youth that there is more to life than youth. And fun. And games.
And that wouldn't be good.