This is my 3rd year, and by far biggest year. my first year I actually started about a year and a half before my first display. go through all the forums read as much as you can, get the software learn it... you need to become an expert in it to use it properly. For about a year, I read nearly every thread and post to gain the knowledge to make it as easy as possible.
first you need to decide if you are going to go with traditional lights or rgb/pixels... look at videos online and find out what elements or props you want to incorporate into your show.
then learn all you can. Don't be afraid to ask what you might think is a dumb question, we were all in your situation at one point. One thing I have found with the countless people on this forum is that there is hardly a question that will go unanswered. Also find people close to your house and talk with them. People in this hobby for the most part are great. Last year I was having an issue and posted about it, a guy messaged me to call him. He sat on the phone with me for about 30 minutes and helped me figure it out.
Always be thinking about what you want to add the next year, The best time to buy stuff is right after christmas, stores have huge clearance sale, also the online vendors have there presales, you can save a lot of money there too. I have already made notes and know what I will be adding next year to the show. Plan early and it saves a lot of money.
Most important is to have fun with it. Depending on the size of your display it will take about a month or so to get everything out and wired up, there will be some late nights and lots of cuts and scrapes. However, the first time you hit play on the software and the lights and music is playing, it's all worth it!
Again welcome to the madness, I hope your family likes christmas music year round...