A mic (or “mike”) should be your friend. And like a friend, you learn what works and what doesn’t when you are working with each other. Mics don’t like to be blown on, don’t like you to get too far away that they can’t hear you. Mics can be sensitive or not, your friend and your foe.
Metaphors aside, begin with a mic you can afford. Purchase one at a store (try Best Buy before Chuck Levins) so that you can hear what it sounds like (and forgo the shipping $ and time) or purchase online through a retail outlet, or buy on Ebay if you know what you’re doing (and make sure the seller offers returns).