We used to say this on the basketball court, when waiting for the pool table, or climbing the jungle gym. When it's all fun and games, who's got next is always at the forefront, the cooler way to clamor that "It's my turn!"
But how excited are you to have what's next at work? Are you ready for the promotion and the added expectation and responsibility? Are you ready for next when it comes to increasing your sales goal or working hard to reduce costs, assuming those are what's next for you and your company?
What's next is often scary or ambitious, but it's also what's necessary. The more excited and ready you are for next, the more easily you'll be able to chase it down.
On the court (listen to me, sounding like I'm good at basketball), we watched what was happening at the moment because we had next. We needed to be ready to hop in and accept the challenge when it was our turn.
Next shouldn't appear out of the blue. You should be watching and waiting because it's on its way. If you really want next (and you should really want it), then be ready to claim it, fight for it, and run with it.