RE...believe in it. As engineers, we are programmed to be clear and concise. If you want to "sell" something, if it already fits into that mold and you believe it, all you'll have to do is talk about it...it will come out naturally. Further, it won't come across as a rehearsed sales pitch as it will be genuine. Your audience will receive it as such.
If you try to promote something you don't believe in, you'll come across as insincere. As Mike noted, if you can fake that, the sky's the limit!
Selling yourself is one of the hardest things an engineer can do. Self promotion is foreign to your stereotypical personality. What I've found easiest to do is simply state facts of your experience...projects, results, etc.
Develop your "other brain"...for us that means learning to do something on the artistic side; photography, music, literature, etc. This will give you some "ice breakers" for conversation....generally when conversation is open and fluid, self promotion is unnecessary.
