When I first started working, I was happily learning all kinds of new stuff: source control, working in a team, unit testing, etc, etc. After two years or so, I felt quite comfortable as a software engineer, but I had no idea how to grow further. I have since discovered that the most important thing is to develop your voice, and here is my lightning talk on the topic:
Voice is an interesting word, because it encompasses so many things. It's your vision, your direction, what you believe in and what you stand for. Voice also implies that it needs to projected, that you need to let other people know what you are trying to do.
Others don't know more than you
How many times were you in a conversation, forming an opinion, someone spoke and you discarded your thoughts? The distinguishing characteristic of someone who has found his voice is that he talks. He is using his voice, but that does not mean that he knows more than you. Be aware of that so you can listen critically and form your own opinion.
Delete "I think"
Email is a great way to build up your voice. Before you send out any emails, delete phrases like "I think", "I believe", "Maybe we should do it". They dampen your voice, and make you sound weaker than you actually are.
Reply to group emails
When someone poses a question to your team mailing list, reply. Don't go off and research for half an hour to come up with the perfect response. Just tell them the steps you were planning to take, and the expected outcome. As your name appears more and more on the mailing list, people think about you more, and will start asking for your opinion.
Sit at the table
Your team has regular meetings, right? Don't hide in the back row and bury your head behind your laptop. Sit at the table, and make a presence. Better yet, sit next to your boss. That takes courage, which sends a very strong signal. Also, your boss will probably turn around and ask you for your opinion, so you don't have to shout and wave to get your voice heard.
Learn to say no
To develop your voice, you need to focus on what matters the most, and stay on course. There are a million things that people want you to do, and you need to push back on the ones that don't matter. In the process you will learn to defend your position and vocalize your priorities.
Let your voice lead you
Realize that you have something to contribute, make a presence in emails and meetings, and defend your position. Slowly but surely your voice will emerge. Let that guide your career, with confidence and a sense of purpose.