With the proliferation of mobile devices, it has become necessary for blogs and websites to be mobile-friendly. WordPress is very SEO friendly and it also helps with mobile access.
The easiest way to make sure your blog is mobile friendly is to use a theme that is responsive. The term responsive design refers to a web design that is flexible and self-adjusting depending on the type of device that the blog is being displayed on.
If the blog is visited through a phone, or a tablet, or a big screen on a desktop computer, the theme adjusts itself to fit and function differently according to each environment.
When you find a theme for your blog, make sure it is labeled as a responsive theme. Most modern themes should be and I would suggest you stay away from themes that aren’t mobile friendly.
If you already have a blog and can’t change the theme right away, you can use a plugin like WP Touch for WordPress. This plugin converts your blog to a mobile friendly website on the fly if the visitor is using a mobile device.
One more way you can make your WordPress blog mobile-friendly is by installing the Jetpack plugin (see: What is Jetpack?) and enabling the Mobile Theme feature; this doesn’t always work and sometimes requires additional customizations but it may work for you.