When checking in, always ask for an upgrade. That question costs nothing and may result in a great room.
Always smile and never appear demanding. Asking the simple question of a room upgrade — and letting them know you understand it may not be possible — keeps the clerk in an accommodating mode.
Just a simple request of an upper floor or a room with a great view is a request the clerk can easily arrange. Alternatively, you may end up in a suite.
Upgrading guests costs management nothing (assuming the hotel is not at capacity) and creates goodwill.