AdWords is the most competitive marketplace for advertisers on the planet. You need a bit of experience before you can competently manage campaigns for clients. My advice to you is to hire an experienced AdWords account manager, or sub it out to an agency. That way you can maintain your own reputation, service the client properly, all while you watch over the shoulder of a professional to learn the craft. Otherwise, you are setting yourself and your new client up for a fail.
Having said that, you can never learn anything until you actually start doing it. So if you and your client are willing to invest money in your education then please follow this advice:
Start with a goal that is based on your client’s primary business objective. I can’t tell you how many times people have come to this forum asking whether their campaign stats were good, or bad. Typically they have never even bothered to set a goal, and when asked, it is something vague like “make as many conversions as possible”. If you have no specific goal then you can never reach it.
Let me make an analogy:
Think of your marketing campaigns as a sailing vessel and yourself as the captain of that vessel. If you set sail with no particular port in mind then how will you know if you are on course, or whether you are making progress toward any worthwhile goal?
If you ask the captain of a passing ship if you are on course for your objective, how will he answer you if you haven’t even picked a waypoint?
Launching an AdWords campaign without a clear objective, and no specific goals will leave just as lost as a poor sailor who sets out without a specific port in mind, nor charts to guide his journey. If you have a clear objective, and a specific, measurable, and time-bound goal for your campaigns then at least you will know if you are making progress, or just lost in an ocean of competition where you will eventually sink, taking your client’s business with you to the bottom of the sea.
Don’t be that idiot that goes out and sinks his boat, taking his paying passengers down with him, just because he didn’t want to hire a competent captain to man the helm.