If your company is small enough and you have an office, the best thing is to create a sign that's displayed prominently in the common space for everyone to see and absorb. I know a few companies that have used always-on monitors or even projectors to display key messaging for employees and visitors in common spaces. I saw a photo once of Facebook's early office and it had mission-related quotes above their door frames. That's a good idea too. In their case is was something like "move fast and break things" which underscored their appetite for innovation and risk.
If your team is distributed, you'll need to find a prominent place to post it in whatever software you use for collaboration and project management.
In the end all what really matters is you make an effort to highlight the mission. It can't be something you work on in an offsite and then stick in a PowerPoint that you share in one meeting and never see again.