I am sure the question when should I actually start using Drupal 8 has been been asked many times. Depending on who you talk to, you may get a different answer any time you ask. Here is what Acquia is saying in their article on Drupal 8 titled “The Ultimate Guide to Drupal 8” The article/white paper is very long and includes a lot of cool Drupal features you may not be aware of. Check it out for more details and start learning
When Should You Actually Start Using Drupal 8?
“If you’re a module developer, you should start caring about Drupal 8 right now. It’s still possible to provide useful feedback on APIs and ensure Drupal 8 ships with everything you need to get your projects ported. But bear in mind that some of Drupal 8’s APIs will still be changed before release if needed to fix critical issues, so you may still need to make code adjustments post-RC.
If you’re a documentation author, translator, or designer, note that Drupal 8’s user interface, interface text, and markup are not finalized until the first release candidate, so you’d want to wait until RC1 to focus heavily on user-facing documentation, translations, or themes (though by all means, adventurous contributors should start now to provide feedback while we can still fix things).
If you’re an early adopter Drupal user with developers on staff who don’t mind porting modules and fixing core bugs along the way, and have a launch date in late 2015 or 2016, you may want to start building your D8 sites once Drupal 8 hits a late beta or a RC. This would be a particularly good idea if you need some of the features Drupal 8 offers.
Most users will want to use Drupal 8 a few months after Drupal 8’s release, when various contributed modules are ported. Keep your eyes on the Drupal project usage graph. When the D7 and D8 lines cross, it may be a good time for you to make the jump, because it means there are more D8 users than D7, so most of the hard work has been done for you already”
So What Should You Do in the Meantime?
To answer this question, I found https://www.acquia.com/blog/getting-your-site-ready-drupal-8 with an answer I will give to anyone who will ask me the same question.
Use Drupal 7. Drupal 7 is a stable, mature, robust, powerful, well-supported framework which will be maintained with bug fixes until after the LTS release of Drupal 8, and supported with security fixes until Drupal 9’s LTS release (several years from now). And a number of the great features in Drupal 8 are available in Drupal 7 as well, with contributed modules.
While using Drupal 7, you can start preparing for Drupal 8 by using some of the Drupal 7 modules that are now part of Drupal 8 core.
Here is a list of some important once. You can start using these modules now if you are not already doing so in preparation for Drupal 8;