Attached is a graphic showing search positions for my keywords after three months of doing nothing to keep them up at <snip>, i.e. down a total of 278 positions! There are three sets of keywords. The first is for general industry terms, the second two are for specific niches (seeking culture, and seeking outdoor experienced).
I can no longer do this SEO work myself, and am looking for someone to help with it. But first I need to know what is the latest best practice after Google's recent changes. Any thoughts?
As mentioned by the TechnoBear, the problem could be with any of the updates effecting your website. So first try diagnosing the cause of the problem and then attend to it. You could scan your content in webpages for optimal keyword density and proximity. You could also possibly scan your links if you have used any spammy links pointing to your site. Another reason could be that other sites have improvised on their optimization techniques and therefore your site could have gone down, but since you say its by 278 positions, i suspect something could be fishy with the SEO of your site.
I would suggest you to resort to is on-page optimization on the search engine guidelines. This will help you have a better chance of being ranked and once you are done with on-page you can put your efforts for off-page optimization as well as also make your presence felt in the social media circuit. Hope that it proves helpful.