I always sleep well on public transportation, bus, planes, train. 
The tip to have a good sleep is that I always have my jacket so i can cover my face and sleep tight. 
My best overnight experiences was the night bus from Nagoya to Tokyo. The bus quiet and clean, with a free blanket and toilet. 

One time, I remembered i even slept on the boat after scuba diving, but that time I put my towel to cover my body. haha 
 

I can sleep on overnight buses and planes. Also I like to nap when catching buses and trains during the day too.

To get to sleep I close my eyes, then focus on my breathing for a few minutes before relaxing more. Sometimes you need to adjust the headrest, or slump over a tray-table so you do not suddenly wake up from falling, or banging your head on the window or your seat partner.