How to make easy holiday parties? - by letting others share in the work! (In fact, this has the potential of making more complex parties as easy for you to bring off as simplistic ones... so that you might find your entertaining repertoire growing without the anticipated strain on your nervous system.)

It isn't logical to assume that the host has to do it all. Remember that not everyone feels up to coordinating a party - and so most will be grateful that you're providing them the opportunity to enjoy the rest of it. I think you'll find that a goodly percentage of them would love to only help. (After all, if you host the party, it may mean to them that they won't have to - whew!)

Allowing guests to bring "potluck" food dishes to the party makes a lot less work for the party-giver. ...It might also be very pleasing to those guests who enjoy preparing food. Even if you enjoy party food preparation yourself, you can always supplement with some offerings from guests - at least the guests who ask if they can bring something. (And if you're not totally comfortable with an outright yes, you could say something like, "Sure, if you’ll promise not to worry about it if something comes up to make it a lot of trouble.") 

The simplest menu for cleanup is a finger food buffet - all you need is small plates or wide, shallow bowls; maybe you don’t even need any flatware at all! Once you get into casseroles, soups, ice cream, etc., the dishes to wash (or buy and throw away) mount. Full-on dinners are possible as finger food (knishes, stuffed croissants, frittata squares, veggies and dips, cookies, etc.) - but add in forks, and the variety grows amazingly, even for foods that can be neatly cut into per-person pieces. And such meals are always popular with guests, because they're fun like picnics.

But speaking of dinner, all parties don't have to happen at night! You could have a box lunch potluck, where you exchange them  as though they were gifts. (You could even follow the example of the old-time box lunch social, where the meals, prepared by the women, are for two, and are bid on by the men... who then share them with the cook. ...And the money goes toward a charity of some sort.) 

Then, of course, nothing is to prevent you from sharing the job of putting on the whole party! If the thought of planning, inviting, hosting, cooking, decorating, cleaning up, etc. puts you in an agony of dread, call up a friend or two - they might be in the same quandary! Link up, and you’ll each have more fun before, during, and after the party (the "during" part being the most important - you need to enjoy yourself too!).

Theme parties can be devised so as to lessen work too... Many people wish to receive holiday cards but dread having to send them! Why not consider a "card party"? ...Wherein all bring their cards and address books and get the addressing out of the way in a companionable fashion. ...Or make the cards there.

Some people have trouble getting going without a kick-off to the holiday season... An early Christmas party will get everyone in the right mood for their own holiday "chores" and amusements. 

Make decorations, perhaps.  You could make ornaments as a family one night, to be handed out to house visitors throughout the holiday season. Or invite friends over to make ornaments to sell for a fundraiser.

Or make gifts, or wrapping paper? Or make it a cookie exchange, so that everyone will be prepared to share with their own neighbors and guests later on.

At the very least, you can throw a party yourself but be prepared ahead of time to dole out some simple but useful tasks to those who ask what they can do to help - and would probably truly love to share the load. Your "to delegate" list could contain such things as:  be in charge of punch refills; open the wine bottles; toss the salad; carve the meat; serve the coffee; keep the music going... whatever you know needs to be done to make you feel good about your fête, but you don't have to do yourself. (And there's always the dishes... And if you arrange to collect the silverware separately from the dishware, you can ask someone to wash just that! - and another person the cups... and another the plates...)

And when the party is over, and you dread trying to stuff all the leftovers into your groaning refrigerator... don't! Be ready to send leftovers home with your guests - by having on hand plastic zip bags for dryer foods, paper takeout containers for slurpy dishes, and extra jars for drinks. Good for everyone!