This is an excellent question!

There are a number of things you'll want to keep in mind when building out your posts and pages if you want to be successful with the mobile first index.

Before I get into it though, think of this the same way Kyle teaches SEO - you don't want to serve up different experiences based on how someone is viewing your site, just like you don't want to try and write for the search engines. Always think of the user first.

Now, some tips for the mobile-first index:

Buttons - make use of large buttons when possible. People should be able to clearly and easily click on your buttons. This is especially important with items like slideshows that may have buttons in them.

Content - Keep your paragraphs short. Aim for 3-5 sentences per paragraph and try not to write long, run-on sentences. Imagine reading an article on your phone and suddenly a paragraph takes up your whole screen.

Above all write naturally, but try and keep paragraphs short.

Additionally, lists are still your friend.

Images - Try not to overuse images and make sure your images are optimized so they load fast. Use a plugin like EWWW (which you should already have if you built your site through WA) to compress your image sizes.

If possible, use icons instead of images. Graphically, they still look nice. They also load a heck of a lot faster.

Themes - Make sure your theme is mobile friendly. Whether it has a mobile version or is responsive or adaptive. Just make sure your mobile site doesn't look like a scaled down version of your desktop site.

Plugins - There's a reason WA tracks and grades your site's plugin count. The more you have, the more weight your website holds. The more weight your website holds, the slower your load times will get. (This also applies to themes. If you get a theme with a million features it will look nice, but also likely be bogged down by the code put in to all those features. It's all about balance)

Ideally you want your pages to load in under 2 seconds on a 3G network. Take your phone off wifi and test your load times that way.

I'll write a more in-depth post on this later but those should be a good basis to get you started.

**After hinting at it for a solid 3 years**