The way you live your life, your conduct and your character can often serve as a GREATER witness of your faith to others than ANY words you could ever say, and done that way, you don't have to trouble yourself with finding the right words to express your belief to others.
But as the Holy Spirit moves you, TALK, and share that Word!! God did not give believers a spirit of fear! But, if you sense that someone is not interested in hearing what you have to say, back off. You don't want to push your faith down people's throats.
It's ultimately God who will move the hearts and minds of men.