Prathesha,
The best way to improve vocabulary is reading. As to your new words, I'd say first learn to use them in the regular way, before you start to innovate
Once you've learned a new word, maybe you can visit the Cambridge site, and memorize how it is used? Or google the word, and see in which contexts it is used.
Then yes, you're right, eye-contact is important. But if there are really many people in your audience, you can hardly make eye-contact with everyone. If you're not shy, you can try it.
If you are, I think it's safer - for you - to target on a few friendly-looking persons.