Don't park in the Disneyland parking lot. It's overpriced. There's neighborhoods nearby to park your car where it's free and the car will be safe.
Go to Disneyland on a Tuesday or a Thursday. Less people go on those dates and you can walk right on rides. If there is a line on those days they're shorter than the regular days. The most I had to wait in line was about five minutes on Tuesdays and Thursdays.
Bring your own lunches. If you do buy food in Disneyland you should get the Gumbo in New Orleans Square because it's cheaper.
If you like desserts go to the vender who sells ice cream near the Tiki Room. They sell pineapple ice cream that's in pineapple juice and it's delicious.
Try to go on Space Mountain earlier. That line is always long.
Go in the morning right when Disneyland opens. People tend to show up there after school or in the late afternoons.
If you have enough money for both parks, go to California Adventure as well and get the park hopping passes. It costs extra but there's a lot to do at both parks. California Adventure is the only place where you're allowed to drink beer and there's none of that allowed at Disneyland.
DON'T stay at the Disneyland hotel. Unless you have a lot of money. Stay at the nearby hotels that are cheaper.
Wear the correct footwear. Don't wear sandals. Wear boots or sneakers. You'll be walking for 8-10 hours and your feet will hurt all day. I see so many people at Disneyland wearing the wrong shoes all the time.
If you like souvenirs either get a Disney hat or the pin buttons. They're the coolest ones.
The Peter Pan line is ALWAYS long no matter what time or day you get in. If you want to go on that one for fun, do that one earlier to get it over with.
Take advantage of the Disneyland train. It'll get you around the park easier so you don't have to walk much. There's also a cool dinosaur thing you can watch when you ride the train.
https://youtube.com/watch?v=AmYuU9hS6pc