I think this is a 2-fold question.
The first is how do you come up with the money for a vacation. I've always believed in the importance of taking at least 1 week-long vacation every year (I used to be able to do 2, but now it's down to one big one in the fall and a smaller one in the spring/summer), so knowing that you're going to do it, that money should start building up right after you come back from the previous vacation. Whether you set aside a separate account or merely keep track of additional money that you're putting in your savings account specifically for your vacation, that saving should start immediately. Ways to save that money can come from cutting unnecessary spending from your budget (nights out, fancy dinners, gifts, Starbucks, etc...), while other sources may come from your annual raise (if you get one), gifts, or a financial windfall. The important thing is that if you know you're going to spend money 12 months from now, it's easier to start now than it is 10 months from now.
The other way to save money is by making tough choices about your vacation. You should ALWAYS have a budget, and even if you feel a Disney vacation is a once-in-a-lifetime type trip, you should still set boundaries and a limit to your spending. I'm not going to tell people how they should spend their money, but I know I try to keep my 3-person 7-10 day Orlando trips in the $2k-$4k range. However, we tend to go every year or 2, so splurging is not as important for us. Now, there may be different considerations based on what you want to do or how long you want to stay, but you should definitely set a top number, and do whatever it takes to keep from exceeding it, and that includes food, souveniers, and park admissions (in addition to the travel and lodging). You can save money before you even book by actively searching deals. If you're flying, use Kayak and other fare aggregators to understand how much your airfare will cost along with the trends in pricing. In most cases, you will want to book airfare between 30-90 days prior, but some routes have high variability that result in super cheap fares closer to your departure (if you're willing to take that chance). Also, don't be afraid to call the airline if you pay for tickets and see the price drop 2 days later. While many won't give you that difference, some will, while others may offer you a free bag or other cost deferral.
When it comes to lodging, look around, and be willing to shop for the best deal. Make sure you're considering everything about a hotel. For instance, while Disney hotels don't provide breakfast, like many off-site hotels do, they do give you free parking at all of the parks along with Magic Hours and the new benefit of booking Fastpass+ reservations ahead of your arrival in the parks. Some people like having a hot breakfast, so that room at the Holiday Inn Express could be worth as much as $30 or more to a family of 4 over staying at a Disney hotel. However, if your family doesn't mind cereal, yogurt, or fruit for breakfast purchased at a local grocery store and stored in your room fridge (not all Disney rooms have a fridge though, so check first), than losing that free breakfast may not be that big of a deal when considering the perks of an on-site room.
You should always compare off-site to on-site, and make sure you understand all of the pros and cons of the different hotels. Understand that most off-site hotels that advertise a free shuttle service to the park that you will be held hostage to the times of that shuttle, or be forced to take a cab. Off-site hotel shuttles are notorious for taking guests to the park at or slightly after rope drop, and picking them up shortly after the last fireworks show of the day, which may be an hour or more before the park actually closes. Personally, I don't even consider an off-site hotel shuttle a perk in most cases, and assume that I'll be paying $14/day to park my car at the parks. Also, don't be afraid to stay in multiple hotels during your visit. If you want to get the perks of a Disney hotel while visiting their parks, that's great, but those perks are worthless at Sea World, Legoland, and Universal. Sometimes it's nice to stay in one spot for an entire vacation, but you can get significant savings in money and/or perks by changing rooms throughout your vacation. Also, note that some hotels (especially on-site) charge significantly more for rooms on weekends than weekdays. You may be able to save quite a bit of money by staying at an on-site hotel Sunday through Thursday, but then switching to an off-site hotel on the weekend. Also, don't be afraid to search around for vacation rentals and/or local homes that natives rent to tourists. Those vacation homes can save families a lot of money if you need multiple rooms or are traveling with multiple families.
Just like airfares, don't stop checking the rates after you book. While it's rare to see hotel rates drop as your vacation approaches, many chains will offer specials, and the Disney hotels will typically offer free dining or other discounts when booking certain rooms during certain time periods. If you book before a discount or promotion is announced, don't be afraid to call and ask for the discount to be applied to your reservation, or be willing to cancel your existing reservations and rebook using the promotion. Most hotels do not charge for cancellation, and while you pay a deposit from a Disney hotel, it's pretty easy to call and have them chenge your reservation to apply the promotion.
When it comes to spending money in the parks, set yourself a daily budget for food, gifts and admission, and stick to it. Always have an extra stack of money available for those can't miss experiences or gifts. Don't think that you can splurge on something today in the hopes of saving money tomorrow.