I'd say checklists. It's much easier for me personally to define what I need to do (the definitions can be vague but need to be set) and then act on it. If the checklist items are not defined then the chances of getting distracted after completing one task are very high.
People around me, actually!
I thrive the most in environments where a lot of (preferably like-minded and ambitious) people are around me, like in co-working spaces, offices or Uni libraries, because there is just a sense of productivity in the room and also the small chats help me destress from my work. :)
@sophia_buttgen I have never thought of it like that but I agree! I work from home but I find myself going out to shared working areas to actually get some work done! Well said, Sophia, thank you!
Music!
I go from classic, to punk rock, to metal, to pop, all depending on the work and kind of focus I need. But usually music is a must if I'm out of meetings :)