10 Ways Theme Choice can Impact SEO (Online Marketing)?
1) Page loading times - page speed is important - minimising calls, incorporating CDN's, and other practices for reducing loading times is a key part of a good theme
2) No use of mixed https and http content - go one way, the other or // neutral, but don't mix and match. SSL may be slower, but it is considered the gold standard at the type of this post.
3) Use of semantic markup for html5 - things like header, main, nav, section, article, aside, etc
4) Use of structured data - though hard to quantify in benefits, why not make it easier for search engines, by marking up your addresses, and other key bits of information, using search engine friendly markup
5) If using WordPress, or other common platform, bundled plugin choices - the right plugins - and not too many of them weighting down a site unnecessarily can be key to speed optimisation, ease of maintenance, security, and behaving as expected (plugins doing what they should do). Most popular is not the same as best, otherwise McDonalds hamburgers would be considered the finest in the world... Yoast is the McDonalds of SEO plugins - largely due to his unending love for canonicals, despite being proven time and time again that they cause more messes than they fix - especially when 301's are an option instead.
6) Mobile friendly - if it isn't mobile friendly out of the box, then one can't expect a non-technical site owner to 'whip up' a mobile friendly version, plumb it in and make it all work seamlessly together
7) Social Sharing - it's gotta make it easy for people to share with those they consider important to them
8) Easy Calls to Action - if someone has to find a button every time they want to make a call to action, then you've done them no favours. While this isn't organic SEO, it is important to the online marketing success of the site, hence the reason I've included it. Newsletter sign ups, and the reasons why people should sign up, should be easily inserted into the calls to action.
9) Lead Nurturing - while 8 above deals with lead capture, this item 9 deals with lead nurturing - once you get their email address and interest, have you made it easy for them to be notified when new posts appear in a category of their interest, have you made it easy for them to be notified of any new products, certain keywords mentioned, notified of contests won, or just kept in touch with when you regularly publish a newsletter every couple of weeks.... Built-in marketing comms and/or integrated marketing automation is one big difference that separates most mom and pops from the top brands they want to compete against.
10) Analytics - conversion tracking needs to be a pre-planned activity, not a bolt-on afterthought. People want websites because they will bring in new business. If you aren't able to measure those who convert, where they came from, what page they were on, what button they clicked, what videos they saw, what contact form they filled in, as well as those that didn't complete the contact form, then you've effectively built a blind site - one that hamstrings the site owner before they even get started in the world of online business.