The best advice that I can give is to not become overly restrictive. From what clients of mine have said, it sounds like those that try to be the most strict tend to do the "worst" over the holidays. If you go into each dinner or gathering with the knowledge that you will have a few sweets or other not so ideal foods, but set a limit, you'll probably be much better of than if you try to stay away from them completely. The more you say to yourself, "I'm not allowing myself to have any of _____," the more likely you are to not stop thinking about it all night until you binge.
Set yourself a limit and try to balance things out by making mostly healthy choices, but allowing room for some goodies as well. Some people go by the 80/20 rule... follow your plan 80% of the time, allow 20% of freedom. Some days that 20% will just end up being healthy choices anyway, but it's good to let yourself have the guilt-free freedom to have some of those things that you enjoy, but aren't that great for you.
One tip if you are taking food to someone else's house is to take healthy food. That way if there's nothing healthy there, at least you can eat what you've brought with you (like a veggie tray, for example) and have a few tastes of the other stuff.
