That depends completely on your application and on the database. Never set max pool size to more connections than the database can handle. Set min pool size to what the app needs when it is mostly idle (has very few users).
The only way you can find out what those numbers are is to do some load testing, and also monitor the number of active connections of a period of time, such as every 5-15 minutes for a week or 2. After you do that you will have enough information to set the min and max pool sizes.