You're not describing what performance problems you are seeing. Start with updating your question with that.
There are no magical SQL maintenance jobs that will shrink your documents etc, you have to design your SharePoint farm in the correct way to handle large amounts of data.
- Use Site Collections to be able to spread the data over multiple content databases
- Check you versioning history settings
- Check how much data there is in your content databases, don't go over 100GB per content database is the normal recommendation
- Avoid adding all files into a single document library
- Check you SQL I/O performance (disk read/write etc)
etc etc - there are a gazillion ways to tune and design for performance. To further be able to help you please describe how your environment looks like.