Luckily, cleaning it is super easy and goes hand in hand with washing your sheets -- take those off and toss them into the washer/dryer and vacuum the top of the mattress. Take some baking soda and spread it across the mattress and rub it in. Let it sit for about 10-15 minutes and then vacuum it all back up.
This will have your mattress smelling fresh.
For a deeper clean, add cleaning vinegar to a spray bottle and spray it across the top of the mattress. Use a thick bristle brush to rub out locked in dirt and grime. Vacuum the mattress and let dry for at least an hour. Then sprinkle your baking soda on.