Stretching, cross and strength training is a good start to taking care of your joints. But it's not where you should stop.
Mobility exercises will not only help your joints, but improve overall health and performance. Plus, they don't take much time to complete. These exercises are different from your stretching routine and will help your joints move throughout their full range of motion, as opposed to flexibility, which is about muscle length.
Try this exercise routine to counterbalance stiff joints, which can predispose you to mobility deficiencies and lead to injury.