Proficiency comes with practice, experience, and time.

I know you probably weren't looking for this but I typed up some advice for no reason:

• Think logically about code you're writing. That is, you shouldn't write a single line of code that you don't understand. I've seen people copy-paste chunks of code from StackOverflow or wherever without understanding it. Don't do that. If you're using something for reference, understand what each line you're adding does. Type it out manually if you must.
• Good coding practices, code architecture, writing good documentation. These things are essential for working with other people. You probably won't have much experience with this right out of college so most people won't hold it against you. Make a conscious effort to be good at this regardless. Writing code for an assignment? Make it readable. Try to document it properly. Keep the indentation proper,. Don't use Notepad.
• It will be easy to get drawn into holy-war discussions about which programming language is better or which text editor is better. Keep it light. Don't spew it all the time. Nobody likes that guy who keeps saying his editor is better or his programming language is better. It's a matter of taste/preference.
• Internships. Do them. They help a lot with learning, especially the things mentioned in the last point. If you do multiple internships, try to do them in different companies. It'll expose you to how different organizations work and it'll give you better options for when you graduate.

Beyond that, if you really really want to commit to it,

• Algorithms and data structures are important. Know how certain algorithms or data structures work, what makes them fast, why they're better in some situations than others, etc.
• Low level stuff is important. Take courses on Networks, Operating Systems, and Databases. Knowing how they work helps reason about how to make things faster, smaller, better.

Okay enough preaching for the day.