1. If you don't use the apps turn it off (put it in sleep)

2. Don't play mobile games too long (intense cpu usage)

3. Turn off the phone

4. Use a phone cooler accessory (it ranges between 10-20$)

5. Download and use phone cooler app (CPU Cooler etc)

Plus tip :

-Remove screen protector from the back (you don't need it unless the back is glass)

-Keep it below 40C degrees

-In summer don't go directly to the sunlight (stay in a shaded area)

-In winter you can use it to cool your phone (avoid water contact)

-Use cold surface to cool and charge your phone

-If your phone overheats make sure to replace it with better model or use safe mode