You cannot safely or realistically sleep for 8 hours in 3 hours
Do not try to replace sleep with stimulants, alcohol, or drugs
Prioritize getting a full 7 to 9 hours as soon as possible
If you only have 3 hours, take a short nap for 20 to 90 minutes
Keep the room dark, cool, and quiet
Put your phone away and avoid screens before sleeping
Avoid caffeine for several hours before bed
Use a consistent bedtime and wake time
If you are severely sleep-deprived, rest and recover later rather than forcing it
If you have ongoing trouble sleeping, talk to a doctor