I agree with the others that bus depots vary and local rules/customs apply.
- In general you will be required to box your bike, and you should bring your own box.
- Now a days you'll probably have to pay an extra $10-$15 dollars for the bike, at least that's been my experience.
- Being friendly and courteous (without being annoying) to all the workers will get you a long way.
- Most of the time you'll be the one handling the bike, which is a good thing.
- Show the bus driver the same respect you would the captain of a plane or ship. After all, they have the same underlying responsibility.
My last bus travel was 2012, mixed carriers (including Greyhound), Bangor-Boston-NYC. The experience was a positive one.