You must be very tired to sleep on the bus. I'm serious it's not just something you can do. For the hard chairs and tiny amount of leg room to be anything near comfortable you must be very desparate.
There are many places to sit on a bus, there are many models of buses. But one must sit, it really doesn't work to try standing up. Usually I prefer to sit upstairs (if there is one). It's much quieter and warmer. On a few bus routes in London, they still have buses with no doors, not a lot of fun to sit on with rain or coldness.
My absolute favourite place to sleep on a bus is the front left of the top floor. Here it is quiet and relatively warm. Also on modern busses there's a little foot-rest.
The most obvious
Going past your stop is always a worry. I usually try not to fall into too deep a sleep. Or I get some kind soul to wake me at my stop. This doesn't always work. Usually I just wake up every twenty minutes or so, that why when I get close, I can stay awake.
This is a big danger. You have to be careful not to lean your head and arm against the window. Many a time have I been walking up woodhouse road after an hour or so against an icy window trying to massage life back into my arm. I usually wear a hat. I get a nice warm head and insulation from the vibration.
Very dangerous. Avoid at all costs. Particularly on the way there. On the way back not so important
Strange Evil People who want to sit down
Often I'm sitting nice and comfortable when some evil one wants to sit down. As I'm a polite english man I usually move my bag (except once when I ignored the girl in question hehe). I usually plan ahead and leave the bag on the floor in front of me
This is the hardest. When you all nice and snuggly warm in a sweet doze and you look up and realise that it's your stop and you have to go out in the cold rain and walk home and get splashed by a bus and then slip over in a present left by a boxer.
Coffee Sleep Sunrise Sunset