One of the biggest mistakes that we see is an AdWords advertiser showing their full campaign with global geotargeting. Typically an account set up this way is bleeding cash and the account owner is moaning about a lack of conversions.
One of biggest concerns when we see an account set up this way is that non-premium markets are sucking out the cash for the campaign and ads are not being shown to the premium market due to global time zone variations.
One of the very first things that we do is to ask the customer to give us percentages of sales from the various global regions. Sometimes we find that 1% of sales may come from Europe and Asia and yet nearly 80% of the click budget is being spent here.
We recommend structuring and account into groups: North America, Europe, Asia & Australia and then assigning a campaign budget for each based on historical sales. We additionally set up the ads to run within the time zone based on local settings so your ads for that region may be only running from midnight to 2:00 pm your time, but prime time in that geographic region.
Global targeting can work for your account, but be smart about setting it up to give you maximum account control.