Jump On Meaning

(idiomatic) To take immediate action regarding; to avail oneself of without delay.

Example: To board a vehicle.
  Jump on a nº9 bus, and it will take you more or less to the door.
  I hate the way she's always jumping on me for the slightest little mistake.
2003 Oct. 28, "Banking Giant," New York Times (retrieved 15 June 2011):
  Community banks can jump on the opportunity to make changes.
2011 Jan. 28, "How Your Name May Cost You at the Mall," Time:
  So later in life, when the Z's — and even onetime Z's who became A's through marriage — see an item they really like for sale or are offered a deal, they jump on it.