Sailing from Miami
Miami is the busiest cruise port in the world and it behaves like it. Nine lines homeport here, the Caribbean and Bahamas run all year, and on a winter Saturday there can be half a dozen ships loading at once.
That scale is mostly to your advantage. It means choice (of line, of ship, of length, of week), and it means competition on price in a way that thinner ports never see. It also means the terminals are busy, and the difference between arriving at eleven and arriving at two is real.
Which terminal matters. PortMiami is a set of terminals along Dodge Island, not one building, and they are far enough apart to matter to a taxi driver. Your line and terminal letter are on the booking confirmation; have them ready rather than saying “the cruise port”.
Fort Lauderdale is a genuine alternative airport. FLL is about 45 minutes north and frequently cheaper to fly into, and the transfer down is straightforward. If you are pricing flights, price both.
Come the night before if you are flying. This is standard advice and it is worth repeating for Miami specifically, because a winter weather delay anywhere in the northern US is the single most common reason people miss a ship here. A hotel night in Brickell costs far less than a missed sailing.