As the meta tags of a website has the priority in the search engines including the Title Tag on 1st than Description Tag and at last Keyword Tag - that has the very leass priority in the search engines and it is basically used to power your main targeted keywords. And for finding the proper keywords, you have to make your research much sharper and have to analyze your competitors also, you have to check the search volume, search traffic for that particular keywords and should also be aware all the latest trends and most searchable keywords in the Google. Some may be used by the visitors and may be helpful to you.