Create a checklist right now. Write down all of the things you think you need to do between now and the day of the big event. Of course, not all parties need a comprehensive list with timing deadlines. For example, if you were throwing an impromptu get_together with your friends, and you were doing a Mexican_themed party, with Mexican food and margaritas, you would want to make a list of everything you needed from the store. Granted, this is an oversimplification of what goes into planning a party, but you get the idea. The list will help you to remember everything you need for your party to be a success. When creating a party planning checklist for a really important event, like someone's 50th wedding anniversary or a retirement party, there are two extremely important items you need to have on that checklist before anything else: the budget and the guest list.
What's the first thing on your list _ The first thing that needs to be done is choose a date for this very special occasion. If it's going to be a surprise for the mom to be you may want to consult with her significant other. He may be able to give you an idea of her schedule and when would be the best time to completely surprise her. He'll most likely want to help and may come up with a way to get her to the party. When the date is established check it off of your list.