Wordpress SEO for small business education website

I'm looking for someone to provide an SEO review of my website and make improvements with a view to improving it's ranking in google for a small number of low competition key words based around " A Level Chemistry". Happy to accept advice on what else is needed in order to improve ranking. Done some work on Yoast but have had very limited success.
I am a small business just starting out so only have a modest budget. Happy to accept a price for a one off overhall, but equally happy to accept proposals from freelancers for a monthly fee.