Each page of your website needs to be optimized specifically for target keywords that you have in mind for that webpage. In order to do this the first step will be to identify keywords that are highly targeted. This doesn't mean that any common phrase that a user might try out can be used. You need to research on keywords that are being tried out by users via search engines. Every search engine maintains a database of all the keyword searches that its users perform. Keywords that has earned the largest amount of user search, are the ones for which your website should preferably be optimized for. The more targeted your keyword is, the better it helps you with indexing.

Single word keywords are used to target general audience.
Eg:
The keyword "Honda" would help attract every user who tries the keyword "Honda" in their search query. This is more general in nature, so should be optimized on a general page that speaks about Honda and its products.

Two and three word keywords would mean for specific targeted audience, as they are likely searching for a product within the general term.
Eg:
"Honda Accord" would need to be considered as a specific keyword for which the page that deals with Honda Accord cars should be optimized for.