Google makes it very easy to spend a lot of money on PPC ads. Too easy, in my opinion. One example of how they do this is they make the default match type for new keywords "broad match." This means that your ads will not only show when people type in your keyword, but also when someone types something that Google thinks is close to it. Sometimes Google gets it right, which is great. Sometimes they are way off, and you end up spending money for someone searching for something totally different than your product or service. Here's how to use broad match the right way.
First, unless you have a very small budget, you need broad match. A large percentage of Google searches happen so infrequently that you'll never brainstorm up that exact keyword. Broad match allows you to capture those searches which brings in customers you would never find otherwise.
However, broad match does open you up to the possibility of getting irrelevant traffic. To rectify this, bid lower on broad-match keywords. If you spend half as much for broad-match keywords than you do on exact match keywords, then you are still getting the same cost-per-lead with broad match as you would with exact match as long as at least half of your broad-match clicks are relevant.
You also need to keep an eye on what searches your broad-match keywords are being matched to. In the keywords tab you can find a "Search Term" report which will give you that information. You can use this to block traffic from irrelevant searches and find other relevant searches and add them as keywords. So that report helps you twice!
So be cautious, but not afraid, of broad-match keywords. If you follow my simple plan they can give you more customers at the same (or better) cost-per-lead.