is it good to repetite the kw twice ? for example for title: wow gold - got wow gold for free. is it better than just "free wow gold" as title on serp?
Write content that "flows" naturally. If you can fit the keyword in a couple of times (without stuffing) then it is pretty good. I also recommend you highlight your keywords in strong or bold tags.
i wanna know if it do better than "one word" to search engine other than human reader if other condition is the same(backlink bla bla..)
Sprinkle you keywords naturaly through out your website, you can use the same KW twice in the header no problem.
Yes you can repeat your kw twice in your title. So in your case you could use "Buy WOW Gold - WOW Gold For Free" Doing so will be better then just saying "Free WOW Gold".
What is WOW? World of Warcraft? World of Warcraft will not stand forever, maybe only 1-2 years later, so you are running a website for a short run?
you repeat your KW but do it with sense? why free wow gold? You can check if how many visitors are searching for that free wow gold? And when you search for that wow on SEs the result is WOW (world of warcraft)? Is that your targeted KW?
Matt Cutts told on his blog that optimize your site for readers not bots. Make it more readable for readers. But yes, repeating it twice isn't a bad idea.
Not to get off topic but With almost 8 million paying players WOW isn't going anywhere anytime soon. That game will be around longer then 2 yrs.
use Latent Semantic Indexing. LSI considers documents that have many words in common to be semantically close, and ones with few words in common to be semantically distant.
On-page SEO is all about optimizing the website itself for users to be very much guided and grounded in the website and as well as for search engines to gather a large amount of information that is relevant for its users.Optimizing titles, Meta descriptions, and headers is already a cliché but will always remain true to every on-page optimization strategy as it does not only make search engines use these data to present in SERP but as well as the ability of users to understand what the website or page is all about by just looking at these important elements in the website