I have 5 keywords (long tail) which I used for my website content. I used each one for 2 times around each 100 words. Now, I heard that if you write with bold letters everytime a keyword is used, you can get a better rank from Google for them. In other words, I heard that this is a on-site SEO tehnique. But, on the other hand, having all the keywords written with bold fonts on all the pages, can be a bad thing for those who actually are trying to read that text content. So...I really don't know what to do... Should I use the bold letter for my keywords or not?