When you want to enter the gym, it is always necessary to warm up your muscles and stretch first of all, let's put a total of 20 minutes.
What I normally prefer is the treadmill or the bicycle, after which based on the large muscle groups you train you start stretching. here I leave you some illustrations
These remain poses to be used especially for the back and legs. very good is also hugging, pulling the elbows, everything must be maintained for 20 seconds, so the muscles stretch, and you can work your best