Of course you want to make sure they are ripe (soft).
Cut the avocado in half as seen here.
In this case, the avocado was so ripe that the pit was really easy to take out. But, an easy tip that I saw on a show once was to hit it with a sharp knife.
When you pull the knife up it should bring the pit with it.
In this case, I needed chunks of avocado. So, I simply made my cuts while the peel/outer shell was still on.
Then I popped the chunks out!
Much better than the old way I did it which usually ended up with half of it being mush!