I've used essentially the same plan for 20 years, as an auntie, and now as a mom. Actually, the same plan whether or not we've got kids in tow.
We leave our Harbor Blvd hotel about an hour before opening wandering toward the gates with no stress and lots of excitement. We like to be near the front of the entrance line, but again, no stress.
If it's the first day of my visit, no matter the time of day, I head FIRST to the Jungle ride. Simply because once, YEARS ago, I realized that was my pattern and it became an important tradition.
Very rarely someone will try to talk me out of this plan as it's more "efficient" to go somewhere else. But, it's my tradition... And efficiency isn't necessarily the goal. Low stress and high fun surely is!! It's now not only my tradition, as I got an email recently... "Will you please explain to my husband that a trip to Disneyland MUST start out with the Jungle ride??"
Other than that, we think about our top priorities for the day usually plan our first ride or two, then we go as the wind blows us... Living the moment is top priority here.
I find that I have the worst time when I try to fuss to much over which lines are long or short. I'm there with people I love, so generally standing in line shouldn't be a big deal. I enjoy the people I'm with. (Except Storybook Land Canal Boats' line. I HATE that line!)
As we get hungry for lunch we head back to the hotel and eat in the room. (Save tons of money this way!!) We then have a mandatory rest period. (Mandatory for those under 18, those over 18 don't need encouragement!)
My 11-year old niece once balked at the idea, so I told her she didn't have to nap, but she had to lay down and be quiet so she didn't disturb the rest of us... Guess who was asleep first??
After our lunch/rest break (length depends on how tired we are and if we want to go swimming) we head back to the parks and stay until closing or until someone turns into a pumpkin.
One main thing we always do is to bring plenty of healthy snacks, so that behavior/stress levels aren't thrown off by blood sugar crashes. Disneyland's often a high-sugar day, so a snack of jerky, nuts, etc. can help a LOT.
Another important thing is general behavior. I've always told kids that there's no easier place to behave than at Disneyland. You're there to have fun. Sometimes you have to wait for someone else to have their fun, but you'll always get your shot. Otherwise, you wouldn't be there. So, bad behavior simply means that you're overtired and need a nap. No worries. You can just go back to the hotel for a nap.
Never had a kid need to head to the hotel for an unscheduled nap, but it's always on the table.
I LOVE staying late in the parks... It's a different, wonderful experience. So we always stay as late as we can. My daughter was able to stay until park close most nights in February, but it was 10:00. Not sure if we'll be able to stay up until midnight every night during our upcoming trip. We'll see.