These tips mainly concern larger, more well known hotels rather than mom-and-pop places. Here are several things that people either don't get or don't think about:
If you book through a 3rd party booking site, don't be surprised if your stay isn't as perfect as you planned. For hotels, the priority is going to be aimed at their members. If there's only one room left due to overbooking, the room will always go to a member of the hotel rather than someone who booked through a third party. If room types are limited, the third party guest will be the first one switched into a different room type. Booking through third parties are definitely cheaper but just know that you could be potentially sacrificing any guarantees that the hotel provides if you book through them.
Going along with the previous tip, join the member program! Most programs are free and even if you only stay at hotels rarely, they will still get you a cheaper rate than normal and you even get benefits at the most basic levels!
Shut your doors! Most hotel room doors do NOT shut all the way when you let them swing shut on their own! There are quite a few instances where I've returned to my room late at night and seen several doors that are open just a crack because the guests haven't pushed the door shut all the way! Stay safe people!
Be nice to the front desk and housekeeping people! This should obviously go without saying but some people just don't get it. They have the authority to give you FREE UPGRADES! If you're pleasant and ask nicely, most of them are nice enough to do everything we can to make your stay better. The worst we can say is no. :)
This one might also sound like a no-brainer, but even if you pay with cash, you still need to bring a card to cover any incidentals that may occur during your stay. Hotels usually cannot let you stay unless they have some sort of insured way of charging you for any incidents that may have occurred in the room, like accidental damages.
Generally, prices will be cheaper online than at the actual hotel. If you walk in the night of your stay and request a room, it will be more expensive than if you booked it online in the parking lot and then walked in to check in.
If you desire a specific type of room, (facing a certain way, near the elevator, specifically 3rd floor etc.) call ahead and request it in advance! Some hotels have the option to insert those requests online, but in case they don't have the option or you book your room over the phone, just ask and you will be MUCH more likely to get that room.
Bonus: If you're feeling adventurous, and are able to stay at a mom-and-pop bed-and-breakfast sort of place, please do! Each one is vastly different with some great cons that hotel chains can’t offer! They’re all great and unique experiences!