Not really a "tip" or "trick" but more of a suggestion... take lots of pictures.
While in Magic Kingdom for example, take pictures of: ride buildings, ride signage, inside rides (if appropriate), store signs, store buildings, from the 2nd level of the train station looking down Main Street USA, the signs welcoming you to the different lands, the wait times board as you enter the hub, Tomorrowland area from the TTA (if it's open), the many gardens and flowers, the palm trees in Adventureland, the Haunted Mansion exterior in black & white, Frontierland streets from the Liberty Belle...
The list could go on and on.
That's the best advice I could give to a first timer... soak in as much as you possibly can, and take a ton of pictures so you can remember what you experienced.