Hi, it is a rare case, when "active" keywords don't give a single impression for a long time. It is well known in the Adwords platform that most of such keywords are considered "low search volume" and are simply switched off, that is, they don't even participate in the auctions.
So, before the first impression the bid should be some average of what your campaign or adgroup bid is, once you get the first impressions you will get a sense of either under or over bidding by checking the position. Before that first impression, it truly isn't very critical the bid you assign as long as it is in line with the rest of your group/campaign/account.