Corrective flexibility is specifically designed to improve muscle imbalances. It includes self-myofascial Release (foam rolling, which I blogged about here) as well as static stretching. (Static stretching is performed by holding a stretch for a minimum of 20 seconds.) This will allow your muscle to relax and elongate. You might want to do a light warm up by walking, elliptical training, biking or just moving the body through different ranges of motion for a few minutes before doing static stretching to get the blood flowing, but it's not necessary. You can also do your foam rolling first and then move into static stretching.
Active flexibility is designed to improve the extensibility of soft tissue and increase the efficiency of your body movement. Instead of static stretching, where you hold a stretch, with active stretching you move through ranges of motion. For example, if you are bending down to touch your toes, bend your legs for a count of 2 and then straighten for a count of 2. Repeat that 5-10 times. The result here is that you are actively stretching and lengthening your muscles.
Functional Flexibility uses dynamic stretching to take your joints through a full range of motion. Examples include push-ups with rotation, single-leg squats, tube walking and squats. This type of stretching is ideal for a pre-activity warm-up (i.e. if you are going for a jog in the park, do this type of stretching first).
The bottom line is, don't ignore your stretching routine! Make it just as important as the actual exercise itself. If you hate stretching (and even this blog entry isn't going to convince you to do it), then at the very least, foam roll. It is a vital part to any exercise routine, and it will help you correct the muscle imbalances that are inhibiting your workout potential. Stretch and Be Well!