Budget
This works similar to Pay Per Click (PPC) where you can set a daily budget, with tolerances, and either set an end date or end when your budget is used up. The more budget you throw at it, the more the advert will be seen but the advert that is displayed isn’t based on who is willing to pay the most. Facebook needs visitors, and people won’t come back if they are bombarded with non-relevant, poor adverts so they put a lot of emphasis on making sure your advert is high quality and relevant to your target audience. Essentially, they want you to bid the right amount, not the highest, but also have good quality and relevant ads so that your ads get a good estimated action rate. Get all these right and your ads will be seen by your target audience.
Defining the objective, the message and the right target audience is key, or you could just end up wasting money. You can do the research to work out the numbers, but you need to define these first.
Competitors
A great place to start and something to keep your eye on is your competitors and what they are up to, as this could really help you define your campaigns and give you ideas as to the most effective approach. Look for competitors who are active and successful, and monitor two or three to gain insight but whatever you do, don’t copy them. They will be targeting your target audience, so you don’t want to send out exactly the same message. Be unique and have fun.