When you decided which keywords you want to use, insert them in your website.
General
Don’t implement all keywords on a single page. Create specialized documents where you focus on 2-3 keywords instead.
Make sure the keywords blend with the text. If you’re not sure about it, ask a second person how the text looks like.
Use the keywords in all important sections of the page (title, meta tags, document name, content).
Keep the keyword’s spelling constant (e.g. singular vs. plural, hyphens etc.). You can ignore lowercase and uppercase; keywords are not case sensitive.
Technical
Use the keyword in the document name.
Use the keyword in the description of the meta tags.
Use the keyword as early as possible in the document.