1. Flexibility is the result of stretching; and an effective tip to improve one's flexibility is to stretch for a few minutes after workouts / exercises when the body (muscles) is still warm. The muscle responds well during stretching when it is warm. If you do not work-out and still want to improve flexibility by way of stretching then do few warm-up exercises like jump rope, jumping jacks, light push ups etc. before you begin to do stretch.
2. Stretching is incomplete if it is not done in right way. It means any stretch should be done by holding the position at least for 30 seconds or more. Holding the stretch position for 60 seconds or so will greatly improve the flexibility.
3. Pace yourself and avoid jerking by all means during stretching. Whether you are going into a stretch position or coming out of stretch position, do it methodically ie slowly with any abrupt movements or forcing into a particular position. It is recommended to do this way to avoid muscle injury.
4. Stretch all muscle groups. Stretching only a particular muscle group will lead to muscle imbalance and do stretch opposing muscles like bicep vs. triceps, abs vs. lower back etc. Most commonly ignored areas are neck, wrist, ankles, calves and feet.
5. Stretch in increments as you progress. It means do not get into hardest stretch on day one. Instead, start simple stretches in the beginning and as you notice your flexibility is improving, add little bit advanced stretches to challenge. Getting into hardest stretch can cause permanent injury or a muscle sprain that may take long to heal.
6. Be consistent with your stretches and do it regularly to improve flexibility. But do not overdo any stretches and keep changing by doing different routines.
7. Stretching can be helpful for tired muscles, it is recommended to include stretching in workout plan. Also, give proper rest to your body by way of sleep. Sleep is the only way for your body to recoup and repair the body. If you are getting too much tired often because you are not resting well. Listen to your body and give appropriate amount of rest.
8. Best recommended time length to stretch is 10 to 15 minutes every alternate day. Another great tip is to stretch for 2 minutes or so before going to bed, this will help relax muscles and aid in good sleep.