With the younger set I think it's about giving them ample time to really talk. The other night we made sure Dahlia (3.5) had the spotlight for talking time at the table and boy, she had a lot to say. She talked about her friends at school and what she did at home that day and even told her daddy "Let me tell you a story" and proceeded to share a story about a school friends thunderstorm experience.
Letting her know it was her time to shine really helped her to open up. A lot of times at the table the adults get so caught up in conversation (My husbands 20 year old sister lives with us so there are 3 adults) and she interrupts to say something and then gets disciplined for interrupting.
And for me... I know Dahlia pretty well. She's with me all the time other then the few mornings she goes to a little church preschool. I think for us it's more about getting her to open up about her feelings and what she is dealing with as a part of our family and at this age it takes some creativity to get them to do that since they don't always have the words to put with the emotions or feelings.
I am also working on learning new things she would have interest in. We get caught up playing the same game (school) over and over again and she could be totally content playing that every day, all day. It's my job to open her up to new experiences so she has new ideas and concepts to play out.
She knows what she wants and she will do whatever it takes to get it. I admire that in her although it can be hard to deal with at times. I know she will use that skill in life. It's just fine tuning it so that she understands to work hard for what she wants but is also willing to compromise when needed.
She is afraid of a lot of things. Mostly the unknown or the made up. "What was that noise?" "Is that a scary monster?" and so on. We are trying to be as careful with this one as possible not to dismiss fears but also not to allow them to run her life.
And another thing on getting below the surface with young ones. Listen when they play. A lot of times they will open up to something through play that they wouldn't just come out and tell you.