Lunges are a simple exercise which can be done in various ways to suit your fitness level. As I have mentioned before, when you are often resting, the hip flexors in particular can become tight. Regular lunges can keep this flexible and minimise other issues caused by tight hip flexors, such as a bad back.
Begin by kneeling, both knees pressed onto the floor, the tops of your feet flat to the ground. Bring your right leg through, so that your foot is in front of you and your knee is bent. Slide your legs apart from each other until your thighs make a straight line which is at a diagonal to the floor (you know what?! Lunges are very hard to describe in writing!). You may need something like a chair next to you so that you can balance yourself. Gently stretch by pushing more deeply into the lunge. Hold for as long as you can; gradually work up to at least a minute each side.
Once you can do that level without wobbling, upgrade your level. You can try extending your arms straight above your head as you lunge, slowly going into a slight backbend. You can also lunge so that your back leg is no longer resting on the ground. Ensure you do not rotate your knee too far around, otherwise you will hurt your knee and hip.
This is a great exercise to throw into your routine. Try to do it when you first get up out of bed, after you have been sitting for some time, or when you feel tight; just as often as you find comfortable really!