Your question is framed pretty broadly without much detail, but, I will tell you what I can
I have attached a document that talks about general practices to increase performance
If you are backing up to tape, I would advise that you increase concurrency to a much higher value that the default of '4'. One of the main causes of poor backup performance is the inability to keep the tape drives streaming, and the constant stopping and starting of tape drives can impose a performance hit of up to 90%
Concurrency is a measure of how many data streams (called Objects, or Mounted File systems) is going to a single device. If you are backing up enough objects, you can increase concurrency to 10 or 15
However, if you are only backing up one or two objects, increasing concurrency is not going to help
If you are backing up to disk, concurrency has to be set to '1'
Check your disk agent system to make sure that there are no hanging VBDA processes. If you see any, then kill them