A pose that is great for strengthening the muscles that support the knee is anjaneyasana or low lunge/crescent lunge. This pose is often incorporated into the sun salutation series or is done before a warrior series.
Adjustments and modification are available. For example, the back knee can be raised or lowered to the mat, depending on the strength in your knee and leg. The hands can be raised, reaching towards the back (as shown in the picture) or they can be pressed together at the heart. Twists are also available in this pose to add some deeper stretches for the back.
This pose is great is you want to release tension in your hips. It is also good for stretching the hamstrings, quads and groin. This pose can also help build mental focus. Holding this pose helps focus not on thoughts but on the physical nature of the pose.
When going into this pose, be sure to align your knees and ankles, keeping them stacked. Your heart should be open, reaching forward and your arms can be raised, reaching back. Breath deeply in and out, embracing the pose and all that comes with it.