Keywords are pretty much a non-issue as they aren't often used by search engines any more, but it never hurts to add them.
Lets look at this product:
http://www.cosmickites.com/freestyle-audio-soundwave-waterproof-2gb-mp3_player.html
Keyword Research
First thing to determine, is what keywords people are going to search for to find this product. Possibilities include:
waterproof mp3 player
water proof mp3 player
soundwave mp3 player
You then do some keyword research to find out what people are ACTUALLY searching for and get some other suggestions, so put these keywords in at:
https://adwords.google.com/select/KeywordToolExternal
Here you can find out how competitive a keyword is, as well as how much it is actually searched for.
waterproof mp3 player is by far the most searched for keyword, but it is also the most competitive, so trying to rank #1 for it will be more difficult. Looking at something like
soundwave mp3 player, there's far less searches for it, but its easier to rank #1, so you need to determine if you want to go for it or take advantage of ranking #1 for the lesser searched for term.
Note, regardless of what you choose for your page title and meta tags etc., you should always optimize for several of these keywords in your content body, and perhaps even have multiple pages optimizing titles for the different possibilities.
Note also that if we had optimized for
water proof mp3 player instead of
waterproof mp3 player we would have been optimizing for a keyword that gets only 3% of the traffic of the word without the space.
Page Title:
Should contain the #1 keyword(s) you want to rank for first:
i.e. Waterproof Mp3 Player by Soundwave
Link Title:
Should contain the #1 keyword(s) you want to rank for.
i.e. Waterproof Mp3 Player
Meta Keywords:
Should list a few of the keywords you want to rank for:
i.e. waterproof mp3 player, water proof mp3 player, soundwave mp3 player
Meta Description:
Should list your keyword first, but also since it appears in search engine results, could be the difference between somebody clicking or not clicking on your link, so some marketing savvy here helps.
i.e. Waterproof mp3 player from Soundwave is a durable, shock-resistant, 2GB MP3 player making it the perfect waterproof mp3 player for listening while playing water sports.
URL:
In general will be similar to your page title:
i.e. waterproof-mp3-player-soundwave
Hope that helps.