How to be more articulate with expressing myself through speaking?

Principle thing, I would think would be to relax. Attempt to articulate initially by using short sentences or phrases that you perhaps have practiced and know well. Yes, most conversations are spontaneous and you 'practice' as you speak, so get into the practice of speaking more frequently. Speech need not be as wordy or eloquent as what you write. Communication is the main function of speaking. If you have no way to express a thought about a particular person, place or thing, simply say, I really can't say; it's the truth. You can always restart the conversation at a later time, after you've had sufficient time to think over the subject.