If you have a Drupal 7 site, start thinking about upgrading to Drupal 8. Since the upgrade process is involved and means having to update your theme or replace it with a Drupal 8 theme, it would be prudent to bundle this effort with a redesign effort, if possible. In other words, if you have been considering a redesign / rebranding effort, you may want to combine this effort with the Drupal to 7 to 8 upgrade. 

If you have a Drupal 7 site, do not undergo a redesign effort without also upgrading to Drupal 8. If you are going to go through the effort and expense of designing a new theme, it may as well be a Drupal 8 theme, if possible. Of course, your site may rely on certain modules that are not yet available in Drupal 8, but it is time to start mapping out an upgrade strategy. 

If you have a Drupal 8 site, keep it up to date with the latest security and minor version releases. This will put you in a great position to upgrade to Drupal 9 with relative ease.

Image Credit: https://dri.es/drupal-7-8-and-9