In Emacs you sometimes need to recall earlier input. If your in the Minibuffer, use M-p to cycle up through previous and M-n to cycle down through later input.
Its similar to cycling through the lines of a regular buffer, where C-p moves you up to the previous line and C-n moves you down to the next line.
M-p & M-n are useful for cycling through previous search strings.
Want to open a buffer? Hit C-x b. Emacs offers up previous buffer. Hit M-p or M-n and you can cycle through the buffers available. Its a little faster than C-x C-b.
Use M-p & M-n anywhere you can recall previous content.
Real time savers.