Answer:
You are referring to the quality of sleep and the things you do before you sleep and after you wake up. It is not possible to get 8 hours of sleep in 4 hours. But there are things you can do to make it feel like you got 8 hours of sleep in 4 hours.
Explanation:
Step 1: Practice Relaxing Activities
This is obvious and you should not be anxious, nervous, full of energy, etc. when you got to sleep. You need to be relaxed and ready to transition to sleep. For example you can read a book, do yoga, write in a journal, etc.
Step 2: Stay away from Electronic Devices
You should stay away from Electronics such as gaming, tvs, etc. If you need to do it for whatever reason make sure your light night is on. Blue light is one of the biggest reasons for terrible sleep.
Step 3: Get in a comfortable dark environment
When it is dark your body will responds naturally and will be prepared for sleep. Get in a dark and comfortable environment when you got to sleep and right before you got to sleep as well. This will help you prepare to sleep
Step 4: When you wake up Exercise
If you can, wake up and run, stretch, get moving in the morning. Caffeine can help as well! You may think it will make you more tired but by moving and exercising your body will become more awake. I also recommend taking a step outside as well. If you can, expose yourself to light.
Hope this helps you! :)