I've had to move a number of cats off my desk chair lately. I should probably open the laptop.
I considered a post about situational awareness, but initiative may cover it.
Once you enter the work environment, you will find yourself surrounded by mouth-breathers: people who stand and stare with their mouths open and wait to be told what to do, even when they're supposed to be the expert. Such people should be ashamed to breathe at all, but, sadly, they are the majority. I have on numerous occasions (not generally in writing) referred to them as sheep, lemmings, or Sunshine.
These folks are both the bane and the backbone of the workforce. Not being one of them should make your promotion a certainty, unless your immediate supervisor also happens to be a mouth-breather. In that case, you are working to impress her boss, and replace her. I recommend practicing competent kindness with co-workers during your ascension and a benevolent dictatorship to prevent a stampede.
The main problem with those lacking initiative is their failure to act when action is required. Whether it's simple inattentiveness, fear of fill-in-the-blank, or contemptible laziness, they will not step up and do what needs doing when it needs to be done. This can be as small as refilling the paper tray or as serious as allowing a customer's issue to escalate to the point of needing a manager. Most "manager-requiring" problems can be solved with the kind but firm application of store policy, unless store policy is "find the manager." In those cases, I recommend finding another job, preferably the manager's so you can change store policy. That's a stupid policy, unless your entire workforce are sheep and completely untrainable.
TT: I've found behavioral conditioning quite effective. Of course, you can put an iguana on a piano, but that doesn't mean it can play.
Initiative first requires you to pay attention to your surroundings. Look for things that need doing, and then do them, whether or not "it's your job." Sometimes it's not your job because no one thought they had to tell you to do something so simple.
At first, it will be small things like getting extra pens out of Supply or answering a call to help check at the front when you normally stock produce, but it will escalate to writing directions for tasks that should have directions, proposing the implementation of rules to save time and/or money/ the removal of rules that hinder productivity, or creating a job for yourself out of things that have always needed doing but no one saw before (yes, I've done that repeatedly. It's wonderful). You are on the ground floor, and your attentiveness here can bring you to the attention of those above you, for good or ill.
Caveat: the reward for doing a hard job well is to receive a harder job to do, usually with no more pay. This is why is it imperative to do all you do for the Lord. Lack of reward here means bigger returns in Heaven. That's not greedy; it's Biblical (Matt 6).
Push button. Receive bacon.