There's a lot of things about being effective at work that college doesn't teach you. At the risk of sounding like a corporate drone (but a highly efficient corporate drone!), here are some that I've found useful.
Document everything. Have easily-accessible references for everything you've done (plans, presentations, decisions, notes, designs, etc.). It helps you stay focused and helps other people understand what you're doing. Next time someone asks you a question about your project, you'll already have plenty of things to point them to.
Communicate. I've found it better to err on the side of over-communication, its helpful to everyone you work with. Similarly, being responsive is also important: a short reply like "I'm looking into it" or "Looks good to me" is better than leaving the person wondering if you even got their e-mail.
Know key metrics and industry trends. This one will be useful when you least expect it. Understanding some numbers (at least to an order of magnitude) can help you prioritize and make better decisions.
Make an agenda. Everyone has attended plenty of directionless and inefficient meetings. Don't be the reason they have to attend one more.
Try it. It's easier to evaluate an idea when you have a public proof-of-concept that people can give you feedback on.
Know your priorities and your accomplishments. This one is more important than I thought. When you work on something every day, it's easy for it to seem routine and to lose sight of (for lack of a better phrase) "the big-picture". Having your priorities top of mind helps you ensure that you're making an impact. Knowing your accomplishments helps people understand what that impact is.