When some keyword is searched in default WordPress search box, it shows the results sorted by date and due to this sometimes more relevant posts appear in last pages rather than appearing on front page’s top results. This article explains you how you can make your search results more relevant by removing the date sorting feature of WordPress.
Add tags automatically rather than manually. Using Automatic Post Tagger plugin by Devtard all you have to do is create a list of tags with related words for each of them and this plugin automatically adds relevant tags when a post is published or updated. Also it offers you the feature to import those tags which are already present in your database and assign them to all posts.