A quick guide to stretching
This is an overview to stretching effectively. Rather than giving instructions on specific stretches, it's an overview to all types of stretches and how to approach stretching in general.
When learning a new stretching position, first get comfortable in it. To begin with, rather than holding the position, work at repeatedly activating and relaxing the muscles you are trying to stretch. Focus on feeling the sensations that are generated as the muscles you are working on activate and relaxe.
The better you can feel and control your body, the easier it will be for you to improve your flexibility.
Once you've learned to activate and relax particular muscles, focus on doing both actions slowly and smoothly. Slowly and smoothly activate. Slowly and smoothly relax.
When you give a muscle a stable end point, it's easier to control that muscle, whether you are trying to deliberately activate it or relax it.
And so, one of the most basic actions that you can do, no matter what position you are stretching in, is to create a stable foundation or anchor point for the muscle(s) you are trying to stretch.
Whether you are working to activate the muscle you are stretching or trying to relax it, or whether you are trying to activate opposing muscles, in any of these cases, work first at creating a stable foundation (or fixed end point) for that muscle.
That is perhaps the most "basic" requirement for improving flexibility. That being said, you may need a bit more than that to get more flexible. That's where muscle control comes in.
While you are holding a stretch, rather than just wondering about how much time has passed, focus on feeling the muscles you are trying to stretch. Also focus on controlling the muscles that can affect the stretch
There are two main types of sensation that you can "listen" for. One is muscle activation sensation. This is easier to feel in larger, bulkier muscles and those, such as the erector spinae, which have more fascicles.
With muscle activation sensation, it tends to be louder when the muscle is shortened, less loud, or attenuated, when the muscle is lengthened.
With connective tissue tension, you generally only feel this when connective tissue is being stretched. You can look for this sensation at the tendons and ligaments at either end of a muscle. You can also look for it within the belly of the muscle being stretched, in particular when that muscle is relaxed (though if the stretch is deep enough, you may feel it even if the muscle is activated).
Muscle control is the act of controlling your muscles, either activating them or relaxing them so that you can get deeper into whatever stretch that you are doing.
You can work at controlling the muscle you are stretching. You can work at controlling the muscles that oppose the muscle being stretched.
You can also work at controlling both.