Keyboard shortcuts I use every day in tmux

^b then c to create a new window

^b then n to switch to the next window

^b then , then [type something] then ⌤ to rename the current window

^b then % to split the current window into panes vertically

^b then " to split the current window into panes horizontally

^b then ↑ to move to the above pane (works for all four arrows)

^b then q to show pane numbers, then (optionally) the number to switch to that pane

^b then ⎇↑ to resize the current pane up (works for all four arrows)

^b then x to kill the current pane (or window if it only has one pane)

^b then [ to enter copy mode, then four arrow keys to move, even past the visible point, which is great for scrolling--I don't use it much for copying/pasting.