I am not a expert

. At the moment have a site where we are getting 100-300 visitors a day. Traffic coming from 60-70 countries. Lots of content which should be of interest but getting noticed in a crowded market.
All kinds of promises from people saying they can increase traffic by 1,000's. Is it just BS or is there some truth to SEO? And how does the beginner see the trees from the forest and separate the truth from the promises?