I often see existing google adwords campaigns that are poorly focused and bring in a lot of impressions, but have a low click through rate.  Basically,  if you use the default keyword matching type in adwords then it will show your ads to a lot of irrelevant searches, costing you by reducing your quality score and by charging you for irrelevant clicks.

The best approach is to start highly focused with tight phrase matched keywords, and then broaden your campaign out. There is a special matching type that can help here in some circumstances. Say we were advertising for a web design company in Huntingdon (we don’t use PPC ourselves by the way). We could advertise for web design Huntingdon, but that allows Google to show our ads in all sorts of weird ways, maybe they’ll drop the web part and start showing the ads for interior design huntingdon.  Seriously,  they might do that, who knows what craziness broad match could throw in?

We could, and usually do, put in a lot of phrased matched keywords, such as
“Web design huntingdon”
“Huntingdon web design”
“Web designer in huntingdon”
Etc etc
And that will bring in lots of relevant traffic,  but it is easy to miss a word combination that people might use and therefore lose out on potential traffic.

By using a modifier we can put a few more constraints in place on a broad search in addition to the above to help.  So,  also add the search term
+web +design huntingdon
And Google will now do a broad match BUT the resulting match MUST have the words web and design in it. So, this eliminates the worst excesses of adwords broad match,  but lets it spread your reach a little wider. In the case it might bring in searches for something like
Web design huntingdonshire
which we had forgotten to cover in our original phrase matched list.

So, in summary, use long lists of phrase matched keywords to get highly relevant traffic, widen that out with some modified broad matched phrases, never use broad matching alone, and – always – get in negative keywords to build even higher relevancy.