For the second advantage it depends where you want to do. If you want to stay a dev and only code then the best thing to do is to master your stack and learn complex things. By doing that you differentiate yourself and increase the barrier of entry. So for instance to learn C++, AWS, Machine Learning, Hadoop ecosystem, webgl... Depending your field and what can be the next big hard thing with it.
Else, the other way is to go up in the hierarchy to be a team leader and maybe to go higher. At first you have been (or should) start to learn how to manage people. You should know how to lead your team when things are doing well but also when things are at the worst. Sometimes you have deadlines that are hard to meet. Sometimes the stress is at the maximum, financially the company is not doing well, or goals and ideas diverge... It's all the experience you need to get to be able to manage these situations and start to be a great leader.
Also you -may- start to learn to master git to be a team leader, to be able to fix the problems, and manage the repo for the code reviews. Another point should be to increase your communication skill, every day by talking with your team, by enjoying to write well written emails and speeches. These books [1] are a good start. And also a last point that I think is important is to start to get financial skills with things like financial management, accounting, and if possible to be able to do simple DCFs...
[1] http://www.amazon.com/Elements-Style-4th-William-Strunk/dp/0...
http://www.amazon.com/Writing-Well-30th-Anniversary-Nonficti...
http://www.amazon.com/Pitch-Anything-Innovative-Presenting-P...
My favorite book about the act of selling (i.e. pitching) is "Pitch Anything" - http://www.amazon.com/Pitch-Anything-Innovative-Presenting-P...
If you're looking for an overall sales primer/bible, your best bet is probably The Sales Acceleration Formula http://www.amazon.com/Sales-Acceleration-Formula-Technology-...
1. Improv classes (see discussion elsewhere in this thread)
2. Vocabulary - sounding "smart" doesn't necessarily mean "using lots of big words", but vocabulary does matter. If your speech is littered with too many "filler" words like "stuff" and other vague terms, you sound less informed than if you use more precise terminology. Having comprehensive domain knowledge in the field your discussing and knowing the vernacular, can help a lot.
3. I think you can learn a lot by listening to, or reading, speeches and essays by great orators and communicators. You can almost think of this as "modeling" in NLP (Neuro-Linguistic Programming, not Natural Language Processing) terms. If you think Obama, or Bill Clinton, or Martin Luther King, or Elon Musk, or Vladimir Putin, whoever, is a great communicator, search out and listen to and read their speeches. Winston Churchill is somebody interesting in this regard, because there's quite a bit of his stuff available online for free.
http://www.presidency.ucsb.edu/medialist.php?presid=42
https://archive.org/details/Winston_Churchill
4. "It's not what you say, it's how you say it." This quote is used a lot in the "pickup artist" scene, and there's a lot of truth to it. Delivery is crucial. This means tonality, volume, cadence, body language, everything. Something as simple as your posture effects how you communicate with other people. There is a lot of material out there on this, but a popular source is something called the "Alexander Technique". There are also a lot of books on body language. And there are voice coaches who can help fix quirks with your voice itself.
5. There's an old saying "the best way to learn to write well is to write a lot and read a lot" (paraphrased slightly). I think the same thing holds if you transform it to "the best way to learn to speak well is to speak a lot and read and listen a lot". Join Toastmasters (or find some other venue where you can speak in public) and start preparing and giving talks and speeches. Then turn around and consume as many talks and speeches as you can, and pay attention to the details of how the people who impress you speak. You can probably find some great TED talks and the like online to model from.
6. It sounds like an outdated idea, and it may offend the sensibilities of some reading this, but your physical appearance matters as well. If you look physically imposing, people have a tendency to be (at least slightly) more deferential and pay more attention to you. There was a book, I think by Bo Dietl, where the author made the point that "You always get more respect when it appears that you could kick the ass of anybody at the table". I'm not saying you need to get Arnold Schwarzenegger huge, but being physically fit has a lot of benefits. Lifting a few weights here and there might be a bad idea. Broad, strong shoulders, muscular arms, a thick neck, decent chest, etc., that give of an appearance of vitality and strength are probably good things to have.
7. Another thing to consider: If you find people have a tendency to cut you off and start talking over you, do not be afraid to make a little gesture (hold up a hand with your index finger, or index and middle fingers, pointing upward) and/or simply say "Hang on, I'm not finished yet" or "please let me finish making my point".
8. To revisit the NLP thing a moment... there's a LOT of material out there on using very specific speech patterns and linguistic constructs to help get your point across, effect other people's mental states, manage conversations, etc. There's book after book on this, but for starters, I'd look for "Sleight of Mouth" by Robert Dilts, "Reframing" by Richard Bandler, "The Persuasion Skills Black Book" by Rintu Basu, and "Pitching Anything" by Oren Klaff.
http://www.amazon.com/Sleight-Mouth-Robert-Dilts/dp/09169904...
http://www.amazon.com/Reframing-Neuro-Linguistic-Programming...
http://www.amazon.com/Persuasion-Skills-Black-Book-Practical...
http://www.amazon.com/Pitch-Anything-Innovative-Presenting-P...
On reflection, the books I got the most out of that actually shaped my behaviour are...
THE PERSONAL MBA, JOSH KAUFMAN
Was blown away by this. Couldn't believe how much stuff I didn't know about. It covers everything you've asked about and more...
It's also written a bit like a Software Patterns/Recipes book, which I love.
I've read the MBA book about 5 times.
http://www.amazon.co.uk/Personal-MBA-World-Class-Business-Ed...
PITCH ANYTHING, OREN KLAFF
You'll hate reading it. It will make you cringe. It's uncomfortable.
But it changed my attitude to business, my products, and deals a LOT. Which is REALLY important.
Applying some of these techniques had amazing results in any dealings with 3rd parties (sales, partnerships, deals). That's because I'm a softie engineer, not a battle-hardened business man. I still read this before attending any significant meeting.
http://www.amazon.com/Pitch-Anything-Innovative-Presenting-P...
HOW TO BE THE LUCKIEST PERSON ALIVE, JAMES ALTUCHER
Covers everything in one way or another...
I keep coming back to the epic rule list in this book. I keep ignoring them in business, then learning the hard way that the list is right. He shares his failures and successes in a humerous way.
It's a real down-to-earth, eye opening book.
http://www.amazon.com/dp/1461120705
OTHER
I'm reading Lean Startup, and have read Made to Stick, Letting go of the words, Ignore Everybody, Spin Selling, and tons more. All good books, but the 3 above were the biggest impact for me on all levels.
Next do everything @coffeemug said :-)
[1] https://www.amazon.com/Pitch-Anything-Innovative-Presenting-...