Create a different ad group for keywords so that the advertisement displayed is as close of a match as possible. For example,
"rent cameras" => "Rent Camera Gear" "rent lenses" => "Rent Camera Lenses" "rent cameras sf" => "Rent Cameras in San Francisco" "rent nikon" => "Rent Name Brand Cameras" "rent canon" => "Rent Rebels and Name Branc Cameras"
Overall, the keywords should match the words in the advertisement.
Auctions are one with a combination of max CPC multiplied by the quality score, which is affected by the CTR. A "good" CTR is ~ 1%. Overly broad search terms, mis-targeted terms, and not setting "negative keywords" all contribute to the ad participating in auctions that it shouldn't, because it's not a good fit. When this happens, CTR goes down. For example, "buy cameras" shouldn't be a phrase for CameraLends, because the site is not for buying.
Basic controls for, "is the search query close enough to my keywords that my advert will be displayed?" Taking into account factors such as pluralization, misspelling, extra keywords, missing keywords.
Consider the keyword "camera rental"
- Exact match: "camera rental" -- low search volume
- Broad match: "canon camera rental", "buy camera", "camera rentals", "rental cameras" -- "buy camera" is specifically bad, because CameraLends doesn't do it
- Phrase match: "camera rental", "camera rental sf", "nikon camera rental" -- keywords in order must be in search query; "rental camera" would not hit
Overly broad or mistargeted ads will still be displayed, but have low relevance and probably a bad CTR, which drives down the overall quality score. Keywords aren't stemmed (i.e. "camera rent" won't match "camera rental") so put in variations as appropriate.
At a campaign level, exclude words that strongly suggest the intent of the query is a mismatch for the site. For CameraLends, that might be: 'repair', 'phone', specific phone models, 'battery', 'store', 'shop', 'buy', 'free' (very noisy keyword).
At an ad group level, you can use negative keywords to ensure that the proper advertisement is displayed. For example, imagine an ad group focused (hah!) on lenses and another on cameras. "lens" and "lenses" would be a good negative keyword for the camera ad group, because we would prefer the user see the lenses ad group.
To diagnose an ad group's keyword efficiency, you can click "Keyword Details", "Diagnose keywords" to see all the search queries that have surfaced this ad. This is useful for surfacing negative keywords or other bad phrases. To diagnose individual keywords, check the box, click "Keyword Details", and then choose "selected".