Stretching is the most common and touted way to increase flexibility and it may be the least effective. Immediate gains made during stretching are a result of stimulating nerves that are also on stretch. Your nervous system will reach a point of over-stimulation and begin to relax. Once relaxed, your muscles are calmed down and therefore more flexible. This process does not change the properties of the muscle. For muscles to become longer, it is argued, takes days, weeks, and maybe even months of devoted stretching.
Soft tissue mobilization (STM) leads to immediate gains in flexibility. The focus of STM is to promote stagnant and temporarily stuck layers of tissue (skin, fascia, muscle, bone) to glide more easily over one another. These structures move together yet are independent. The more freedom between them the more flexible you are. Will these immediate gains stick around for the long-term? Sure! As long as you keep them moving and occasionally get into those once-challenging positions.
A good manual therapist can determine if soft tissues are limiting your flexibility and treat accordingly.
Still feel the need to stretch? Do a warm up to get your blood flowing and stretch in a relaxed manner. Studies show that gentle stretching with mild discomfort is as effective (if not more) than aggressive stretching.