2015 SEO Hit List

A few things you might want to have knocked off the face of your site before 2016.

RDFa seems to be a less favorable choice for marking up new sites with structured data for a few reasons and seems like it is starting to get phased out. Schema.org microdata and JSON formats seem to be receiving some praise by Google and web developers for its ease of use and vast vocabulary.
Old non-mobile friendly templates that don’t consider loading order / speed or microdata possibilities have got to go (or at least be revisited)! Some things will matter more than others when http2 becomes a mainstay. Script / html / image compression will be more important than concatenation of them. Http2 will be able to address much of the prioritization of the requests by nature, assisting it in doing so will be the trick to loading like lightning.
HTTP connections are becoming less desirable in the eyes of Google. It may be expensive, but worth executing the upgrade to https. Google has been expressing its dismay towards non-secure connections in general, because of man in the middle attacks, user privacy etc. New Google developer API’s are becoming more often HTTPS only.
The # hashtags ajax scheme like the one used in wix is now deprecated but still supported, apps can be crawled and indexed, so hashtags are just an outdated way of separating the display and data in the age of coveted microdata. 
That outdated content can be a drag for your site’s useful content. Only relevant content that provides your visitors some value should be on the site. Long gone are the days of having tons of pages for the sake of content actually being useful.
Seek and destroy spammy user supplied links! Moderation of guest blogging and supplied links is of some importance. Google has been trying to get to the bottom of the spammy link farming / content scraping strategies so it is important to be vigil with the outgoing links and keep tabs on their relevancy to the content on your pages. Usually an unrelated incoming link will just not have any value, but it is best to be active by supplying a disavow list of links that are spammy in nature which couldn’t be removed with a request to the linking site. Always do the research in this case, not really something that should be handled in a half-hearted manner!
Flash elements should probably be added to the list of things to be canned, html5 seems to be rightfully taking its place in many areas!