If you can skillfully use Flex Builder shortcut keys it could advanced improve your working efficiency.The belows are some shortcut keys which you should know.

Ctrl-F11: Run
F11: Debug
Ctrl-Alt-Down: Repeat current line
Alt-Up: Move line (or selection) up
Alt-Down: Move line (or selection) down
Ctrl-Click: Go to definition (also F3)
Ctrl-D: Delete line
Alt-/: Word completion (cycles through possible matches)
Ctrl-Up: Scroll up
Ctrl-Down: Scroll Down

Here is a list of keyboard shortcuts that are useful when editing code.

Here is a complete list of available keyboard shortcuts.

Here is a MAC version shortcut keys(by joshbuhler)

Here is a Eclipse/FDT version shortcut keys(by betriebsraum)

David Zuckerman compiled a short list of shortcut keys in Flex Builder 2 that you should check out if you work with Flex Builder.