Hi,
In My option, here are the must do's at Disnland for visiting the first time
Peter pan
Alice and Wonderland
Its a small World
Buzz Lightyear Astro-blasters
Star Tours
Haunted Mansion
Pinocchio's Daring Journey
Pirates of the Caribbean
Storybook Land Canal boats
Please note that I do not go on roller coasters so that is why there are no big thrill rides on this lists.
In Disney's California Adventure the must do's in my opinion for a first time visitor are:
Radiator Racers in Cars Land
Mater's Junkyard Jamboree
Aladdin- A Musical Spectacular
Toy Story Midway Mania
World Of Color Show
Things that I think you could skip in
Disneyland
Finding Nemo Submarine Voyage
Pirate's Lair on Tom Sawyer Island
In California Adventure I think you can skip:
All of A Bug's Land
For the month of October, it can be crowded because of the Halloween Holiday. I would recommend going the beginning of October or the middle of October.
I am not sure when the Diamond Celebration is going to end. sorry.
Let me know if you have any other questions I can help you with, it would be my pleasure. Have a great time and make sure you get A first time visit button!
Pluto1fan