Does Long Tail Keywords increase Conversions? If I put them in content page's header in order to get more attention of my audience.
Getting more attention and traffic isn't going to mean that your conversions will increase. You are getting more visitors sure. But it won't matter if they don't trust your brand or not like your product.
Long Tail Keywords will only increase your traffic not conversions.
Nope they have no effect you are wasting your time if you trying to get conversions.