No SEO campaign or strategy can be successful without this first, crucial building block. Whilst you may be lucky and get some phrases correct, without good keyword analysis, much effort will be wasted.
Keyword or phrase analysis involves using a tool like Google Adwords keyword tool. The first thing you need to look for is search volume - is anyone actually searching for that term? Secondly, look at the competition - how hard will you need to work to rank well for that term?
The next step is to decide which words or phrases (generally, today, you'll be targeting phrases as words are far too broad a match to rank for) you want to try to rank for. High search volume is not necessarily the best - they usually have the highest competition. Often, phrases with medium, or even low, competition still have good volumes and present a far easier opportunity for ranking.
As many as you want! However, for the purposes of good SEO work, you should be limiting yourself to 2-4 phrases per page. When you get too many, the power of each phrase gets diluted and is wasted. For your front page or home page, we recommend a maximum of 3. This is where most visitors will land, however, don't neglect internal pages. These can also rank well if done correctly, and mean, on a single organic results page, you may have 2 or more entries if done correctly.
Once you've selected the key phrases you want to try and rank for, and selected what pages they're going to be on, the job is to carefully craft them into the copy of that page. That doesn't mean stuffing the page full of them, nor repeating them exactly the same each time. The search engines are now good at picking up synonyms and occurrences of one of the phrase words in isolation.
Let's say you're wanting to rank for "Sacramento dog groomer". Google will pick up "dog grooming", "groom", "canine", "groomed", or "pooch", and "credit" those towards what the page is about - Sacramento dog groomer. In fact, this is how they prefer to see it done, and can penalize those who think that repeating their key phrases 20 times is the be-all and end-all.
To add complexity to the job, i also matters where your phrases show up on the page, and what sort of emphasis you place on them. Having them in the Title tag, the Heading tags, bolded or italicized all tell Google that "...these words are important..."
But we're now getting into the area of SEO. You can see more on the page dedicated to SEO, or download our free SEO 101 primer. There's also another page which goes into more details about offpage SEO & SEO backlinks.