And yes, these are rules. They are not open to negotiation. There are no exceptions.
Get your fare out before the bus arrives.
What!? You were surprised the bus was going to be coming? You were waiting at the stop because it's just fun to hang out on street corners? Seriously, get your fare out of your pocket/bag/purse when you see the bus a block away. Don't wait to get it out until it's your turn to get on the bus.
If your fare is cash, get on the bus last.
The rest of us have made the effort to speed our fare transaction for our convenience but also for that of our fellow passengers. Paying your fare in cash is your prerogative, but it also takes more time than swiping a card or using a transfer. So don't slow everyone else down and step to the back of the line.
Remember that you are not the last person to get on the bus.
Believe it or not, other people get on at the stops after you. This is not your car! This means that you should allow space for others to get on the bus. If you take a seat in a forward-facing seat, take the seat near the window if it's available. If you are sitting in one of the most-forward benches, be aware that you should stand and give up those seats to those with movement difficulties before being asked. If you end up standing, stand as far to the rear of the bus as possible.
Practice timely signaling.
This one takes some practice so if you're new to riding the bus, let other people pull the cord signaling your stop if at all possible. Do not signal too early. Especially if you are unfamiliar with the route, you may force the driver to stop where you did not intend and then he or she will have to stop again at your intended stop. When in doubt, signal at the intersection right before your stop. Do not signal too late. Twenty feet in front of your stop is too late. Pay attention! Again, the intersection right before your stop is the ideal place to signal. Perfect signaling is when you, in your seat, cross that intersection. This allows anyone in front of you that has the same stop to signal if necessary and gives those behind you the opportunity to see you signal if they want the same stop. (Corollary, thanks to 90_percent_sure, if your bus makes but a single stop, don't signal. You'll annoy the driver, your fellow passengers and look like an idiot.)
Thank you, fellow bus riders, for your kind attention to these rules.