Hi Jessica,
First trips are extra magical in my opinion. How exciting that yours is in the works! Once you have your travel dates and budget worked out, I recommend clicking
HERE to see if Disney is currently offering any special discounts or packages for your travel dates. For first trips, you might also consider calling to speak to a reservations agent, who can walk you through the various options for your dates (such as dining plans, park tickets and other options). When you are ready, you can call reservations at 407-W-DISNEY (407-934-7639). Disney's reservations agents are incredibly knowledgeable and helpful at helping families pick a package or resort-only reservation that works best for them. I've only had fabulous experiences with folks on the line.
Once you have your resort and dates set, I recommend coming up with a general itinerary of which parks you intend to visit on each day of your trip, and then making dining reservations (up to 180 days prior to your arrival.) I would try to secure reservations at restaurants that are in or near whichever park you are planning on visiting in a given day to avoid having to spend too much travelling to and from your destination.
From there, I'd include any special events (makeovers at Bibbidi Bobbidi Boutique for any princesses in your party, dinner shows, Cirque du Soleil, etc.) Feel free to write back for more specific tips or any additional questions. Happy planning!