Key areas to use the Keywords to optimize the site ranking:
Image Alt Tags
Keywords should be used in the URL, Title & Meta Description initially. As these are what, which is displayed in Search Engines Results Pages (SERP) snippets.
Keywords must be used in the H1 Heading & content of the Website.
Keep Keyword Density less than 2 percent, i.e., don’t overuse the Keywords, it should be between 0.5 to 2% of the entire text content.
Be precise wherever you use the Keywords in the Website. It doesn’t make sense to use the Keywords if it doesn’t fit in there.
You may go for variations like synonyms, relevant keywords or semantic keywords.
Keywords can also be used over the images as ‘alt text’ or ‘title’ of it, but always describe the image in some words in the alt text.