When you feel tight, like after a long walk, or a gym session, or a whole day at work, or after a family trip etc., straight after or in the next couple of days just do a nice relaxing static stretch. Put the tight muscle into a stretch position until you feel a bit of tension and tightness and stay there, breathe deeply and try and relax. When you feel the muscle relax, just stay there for a couple of minutes more and enjoy it. This can be almost as good as a decent deep tissue massage. On the other hand, when doing stretching to increase flexibility, do as above, but when you feel the target muscle relaxed go a little deeper, wait for relaxation, and repeat. If you do it almost daily, after a few weeks you’ll probably be the most flexible you’ve ever been, and your joints will feel better too. Activities like climbing stairs, sitting down and up AND just sitting will feel better(if you’re stretching leg muscles that is).