How to reduce the available space on the db

Hi, My current database size is 300 GB and available space shows 90 GB.

I want to reduce available space of the db and return some space to the drive for different purpose.

I tried dbcc shrink db which is not working for me.

I tried schrinking the log, etc..but shrinking did not help me.

Can any one suggest how to free the available space to the drive.

Thanks