Effective self promotion is really more of a process, rather than an action. If out of the blue you start talking up some specific accomplishment, that will likely stick out as too self-aggrandizing. The approach should be less of "Gee, isn't it great what I'm doing?" and more about demonstrating your value to a wide number of people at your company. You want to build a body of work that showcases how you think and the breadth of your thinking, and ideally goes beyond just project-specific knowledge, because this kind of strategic thinking is really what's going to get you noticed and promoted.
The process starts first with relationships, so the first thing you need to do is build and cultivate relationships with influential people across your organization -- both formal and informal leaders. Essentially you're building a platform of current and future supporters of your work. Somewhere in this range of relationships you're developing, you may be able to highlight some specific things you've accomplished. But the key will always be that what you did has a measurable and impactful result. So if you've generated some significant amount of money for your company or saved it, then you really have something specific to tout. But just patting yourself on the back, and saying 'Aren't I wonderful?' is not effective self-promotion. Ideally, your accomplishments should related to a specific, extra-ordinary opportunity, and be seen within your overall body of work there.
Over the longer term, your goal is to create some buzz about yourself and a reputation for having valuable insights and the respect of senior leaders. You would know you're starting to establish this by the fact that you have the responsive ears of other people, or if out of the blue, someone asks you to join a team or for your opinions about an important matter.
When it comes to effective self-promotion, I think of one person I've worked with who's very adept at this type of relationship building -- he always sends follow-up notes and emails to senior people thanking them for whatever they may have done, and he comments encouragingly and insightfully on big projects that he knows they're working on. Importantly, though, he's careful not to appear too calculating or overly solicitous in these communications -- he simply takes advantage of natural openings and opportunities to make contact. As a result, he's generated a base of supporters far beyond the reach of his formal job responsibilities, and created some excitement about himself at the company. Hopefully you can start to do the same. Good luck.
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