Keyword LengthResearch indicates that the majority of users' keyword searches are between one and five words long and that most users search with multiple-word phrases rather than single-word phrases. (Source: OneStat.com) While it is important to include a variety of keywords to ensure both quality and quantity of traffic, keep in mind that single-word, general keywords such as 'car' or 'mortgages' will be very high traffic but may not be targeted enough, while seven-word keywords, like 'find ways to rejuvenate unhealthy looking skin' may be so specific that no one ever searches on them.The keywords that perform best for you will depend on your specific products and services and how your customers search for them. People may search for mortgage refinancing with just a few words but may search for engagement rings with a longer search query. For example, a keyword targeting serious jewelry shoppers could be as detailed as 'three stone princess cut platinum diamond engagement ring'. As always, it's important to keep an open mind about keyword length and adjust your strategy based on your campaign results.Negative KeywordsNegative keywords, one of the four types of AdWords keyword matching options, can help target your ads to potential customers and increase your ROI and conversion rates. Unlike broad, exact, and phrase match keywords, negative keywords are keywords on which you do not want your ads to run. You can use negative keywords at either the ad group or the campaign level. When constructing a negative keywords list, try to be as exhaustive as possible, but be careful that none of your negative keywords overlap with your broad, phrase, or exact match keywords, as they will cause your ad not to show. For instance, an advertiser for a financial institution that provides loans but does not offer actual rate quotes may want to include 'rate' and 'rates' as negative keywords. However, if he wanted to include 'fixed rate mortgage' in his keyword list, he should not include 'rate' among his campaign negative keywords list.Just as you can use the Keyword Tool to find keyword variations and modifiers for your 'positive' keywords list, you can also use it to find keyword variations and modifiers for your negative keywords list. You may also want to try searching on some core keywords in Google Search and looking at the first page or two of organic search results to find possible irrelevant themes for which you would not want your ad to show.You may want to employ negative keywords to filter out certain searches for a number of reasons:Filter out different products or services: A real estate agent who is focused on selling homes may wish to include not only the negative keywords of 'rent' and 'renting,' but also use the Keyword Tool to find variations such as 'rents,' 'rental' and 'rentals.' Filter out irrelevant searches: An advertiser selling herbal remedies may discover that the name of a particular remedy also happens to be the name of a musical group. In such a case, it would be wise to include negative keywords such as: 'music,' 'band,' 'concert,' 'ticket,' 'lyric,' 'album,' 'mp3,' and the pluralized versions of these words.Filter for serious buyers: A seller of digital cameras may want to filter out research-oriented keywords such as: 'review,' 'rate,' 'rating,' 'compare,' 'comparing,' 'comparison,' and the pluralized versions of these words.Deleting KeywordsMost of the strategies we have discussed involve expanding keyword lists. If you are optimizing an existing account however, it may be equally valuable to delete keywords from your account, starting with identifying keywords that are performing poorly. Depending on what your advertising goals are, you may want to apply specific strategies to deleting keywords.If you are CTR focused, you may want to identify and delete keywords with high impression counts but low numbers of clickthroughs. These keywords may be too general or not relevant enough and are garnering many impressions but very few clicks. If you are conversion focused, you may want to identify and delete keywords that garner high costs but very few conversions. These keywords may be too specific and accrue very few impressions over a long period of time because very few people are searching on them.You can identify extremely specific or general keywords by running a report and either modifying or deleting these keywords.