I use to work there!
Grab your fast pass for Radiator Springs Racers first thing when the park opens (there is a separate lines to get the fast pass, just outside of bugs land). They will "sell out" within the first 30/45 minutes of park opening. You can also get another fast pass while holding onto that one, so you can do Tower of Terror, Soarin' over California, Screamin', Grizzly River Run (although its super cold, lol).
Also, grab reservations to nicer restaurants ASAP, they book up very fast. Some of my favorites are Blue Bayou, Plaza Inn, Steakhouse 55 in the Disneyland Hotel, Goofy's Kitchen Breakfast Buffet also in Disneyland Hotel (great for kids, characters walk around).
Lastly, if you plan on buying a lot of gifts, lots of stores have an option that lets you leave your merchandise with the store or at a separate location so you don't have to carry it around all day. I try to do my shopping in the morning, because it gets crazy busy at night.
That's about it for now, i could go on for hours, haha.