Rest day. Follow the sequence outlined here. Alternatively, attend a basic, gentle, or restorative yoga class. It's useful to study with a live teacher periodically, to ensure you're practicing the poses safely and with good alignment.
After a harder workout. Move through each of the dynamic sequences 5-7 times, and hold each of the static stretches for at least five breaths.
On a lighter workout day. Move through the exercises listed here. Keep your awareness on your breath—it will tell you if you're working too hard.
After a harder workout. Go for three to five rounds of sun salutations, and aim to hold the static core poses for three to five sets of five or so breaths each.
On a lighter workout day. Move through the sequence outlined below, repeating each pose as many times as you'd like. You can repeat the lunges on the second side after each pose, or move from low lunge to runner's lunge on one side before repeating on the other.
After your shorter weekend workout, or on its own. Hold each pose at least five breaths. Be sure your front knee does not hurt in pigeon.
Later in the day of your longest workout of the week, when you're clean, warm, and fed, enjoy these poses. Hold each for as long as you like, at least five minutes, with special attention to resting with your legs up the wall.