I'd respectfully have to say the Moz guide is a little out of date. When it comes to on-page optimization, being really conservative is the key and synonyms are what's killing it.

Conservative

Only use your target keywords 3-4 times in the following places: title, url, description, content.

And I'm referring to the individual words, not the string. So if you're ranking for 'darth vader costume', if you have in your content 'check out his realistic vader gear', then that instance of 'vader' counts.

Synonyms

Awesome for 3 reasons:

• A safe way to avoid over optimization penalities
• You get credit for ranking the synonyms as well

So when you use "Darth Vader Suit", you're getting ranking mojo for people that are using suit.

Other: be careful with your URLs

With the above example, lets say you have an inner page called "best vader costume"

Try to avoid creating URLs like hxxp://www.darthvadercostume.com/best-vader-costume . You're going to get hit with an over-optimization penalty much easier if you're using these keywords in your content, description and anchors.


Hope this helps!

Meta keywords are useless. Don't waste your time with them. "Page Meta title" doesn't actually mean anything.

Meta description is somewhat useful, but you don't need to have anything there. Google will then decide what to show, and it often shows the bit that's best for the current search and thus most likely to get clicked.