The use of plain and simple language for English speaking is better than saying something that is incomprehensible or could have more than one meaning. If the people you are talking to have to ask for a clarification you are not a good communicator. Believe me, as a copywriter I know how important it is to be as simple and plain as possible.
Effective communication both verbal and written doesn’t mean just talking and writing in style. It means saying and writing what the other person will understand immediately. If the person listening to you or reading your mail wonders what you are trying to say then as a communicator you have failed. This is also what makes a difference between leaders and wanna be leaders.
Some Suggestions for Effective Communication
I would suggest reading newspapers (doesn’t everybody advise that?), but it is surprising that not many people heed this advice.
Write! This is a good way to increase vocabulary. Write about the subjects you would like to discuss. Once you have written, Edit! Think of ways you could say the same thing, in a better way. If it is targeted to a particular group of people (not everybody is interested in everything) then try using words that they would grasp faster.
Talk and start conversations. Talk as if someone is judging you on the number of times you have spoken (like a group discussion during an interview). Have an opinion on everything. Your reading should make you better informed and your writing should give you a better vocabulary. Your opinion could carry weight.
If and when people will seek you out just to talk to you or read what you have to say then you are doing good. Good luck!