Not everyone knows that since IntelliJ IDEA 12 the IDE supports so-called Middle matching. It means that you don’t necessarily need to type an identifier from the beginning. For example, if you only remember a part of the name, just type it and IntelliJ IDEA will still find the right matches for you.
One more tricky feature of code completion is support for quick popups such as Quick documentation (via Ctrl + Q, or Ctrl + J for Mac) or Quick definition (via Shift + Ctrl + I, or Shift + Cmd + I for Mac). These popups are available when you browse suggestions in code completion. In many cases Quick Definition info is more useful than even documentation, especially when you are not sure, which method is to use.
Please find the complete article about the available code completion features here.