Character meet and greets

Meeting characters at the park is as easy as waiting in line. Disneyland as designed several character meet and greet areas so you can have autographs signed or get a picture with your favorite characters. You can meet Tinkerbell and her fairy friends in Pixie Hallow, located right in between the castle and Tomorrowland.
In Fantasyland near the castle there is often a character standing around, like Peter Pan.
The main entrance to the park is where you often find many characteres, especially right as the park opens.
Back in Critter country by the Winnie the Pooh ride is an area designated for Pooh and his friends.
The most popular area is the Disney Princess Faire, located in the back of Fantasyland. This is where you can see 4 or 5 princesses at once. The line here is always ridiculously long (60min).
Sometimes characters just pop up in the strangest places, like walking along Main st.

If you are hoping to just see the characters and not necessarily have a photo taken with them, then the parade that runs daily is the best option. All the characters are in the parade, including Mickey and all the princesses!