How to utilize better vocabulary when talking?

There's absolutely nothing wrong with using the word great when talking. Now if you were writing an essay then you would need better vocabulary. Trust me nobody wants to talk to people who keep on using SAT vocabulary that nobody even knows. That would be boring. Even people at work and other official people with high positions who demand respect would not expect you to use TOO high of a vocabulary. Remember people need to be able to understand what you are saying.