I don’t use panes in iTerm often enough and whenever I do I seem to have forgotten the keyboard commands to split and navigate them, so…

• ⌘D – Split vertically
• ⌘⇧D – Split horizontally
• ⌘⌥↑ (or ↓, ← or →) – Navigate between panes
• ⌘⇧↩ – Maximise pane toggle