Your competitors websites that appear in the top 10 or 20 (or so) places for the target keywords. You need to study their sites. Also the search results pages in question to (including the ads text)... Oops sorry I misread that as "researching" did my answer still make sense or did you mean something else?
I know the best way to search keyword through Google's keyword tool, but don't know the real technique which keyword is the perfect for my website
Like I said you need to study your competitors websites. This is how to find which keywords and learn how your compeition is using them ad then you need to work out the best way to better them The object being that each page is mainly targetting a keyword phrase and you are competing with those competitors to provide the best adnswer with your content. You won't find much that is of use to you in this regard using the Google AdWords tool other than some search terms to check to go and then do as I have said you need to do (IMHO).
Both are important, but I consider mandatory to have a very good on-page SEO. I think that without on-page SEO is totally useless to work on the off-page SEO...
depends on what type of website you own.. both are equally important depending on niche and type of website
OK so you have a website right? You know what said website sells!. Search using Google those things Write down what you use to search as you do so. Those things you used to find your "competition" are also some keywords Now when you see your competitors websites study them and see what they are doing to target the things you have and learn from them. Same for the search results pages themselves. Look at the top page(s) study it(them), look at the links you see and the descriptions and also the ads. Study, learn, then provide better than your competitors. There is no short cut or better way than providing the best most relevant content.
If you site is seo friendly and your content is fresh and unique you can easily promote by search engine with doing seo.
Hello, Both techniques are needed for best results but on page seo is first step if you doing right on page seo then you can easily get the result with some off page techniques.
ON page is most important factor..keyword selection is most important part of On page SEO..So, make sure that you are choosing low or medium competitive keywords with high local and global searches, as these keywords can be easily optimized..
And "email marketing" is what part of "SEO" exactly? Email marketing is not even part of "SEM" which SEO is a part of. Email marketing is not SEO... Though lot's of so called SEO's spam the heck out of masses of peoples inbox's every single day annoying the heck out of everyone with these unsolicited lists of crap generic services they reckon will help people with SEO when the only thing it is likely to help people with is making their pockets or wallets a bit lighter..
Email marketing can be used for building brand name, and it would attract returning visitors to your site which is going to help in SEO too.
Yet it still has only very little to do with "Off site SEO". Just a very small metric with thanks from emailing but thta is eMail marketing so not really "of site SEO"...