Of course, it is always helpful to check the weather before you leave your hotel or home. If the day is sunny, make sure to put on sunscreen and bring a bottle with you. You might want to wear a hat if you are particularly sensitive to sun. Also, wear comfortable walking shoes. Not only is the park big, but you likely will be doing a lot of standing in line.
If possible, get to the park when it opens so you can ride the main attractions before they get too crowded. Many people show up after lunch, so you can avoid long lines if you arrive early. Also, research the park's website before you arrive so you can prioritize what shows you and your group would like to see. That way, you will know exactly where you need to be at a specific time so your group can meet up. Keep in mind that certain rides require minimum heights, so measure your children beforehand so you know what rides they can enjoy.
When many people enter the park, they go to the attractions that they see first. Then, they work their way around the park. If you want to beat a lot of the lines, find a spot near the end and work your way backward.
If a big, popular show is going on and you have either seen it before or can afford to miss it, you can take advantage of the shorter lines and quickly make your way through rides. This theory also works for lunch. If you can avoid the main lunch and dinner times and eat slightly off schedule, you will save a lot of time waiting to order.
