Stored procedure tuning is the same as query tuning. You measure the performance of the procedure, in terms of time to execute, logical reads and CPU. You make modifications to the procedure or the structures that the procedure calls, then you measure again. Repeat as necessary. Follow the link to my book. I detail this process and more.
"The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood"
- Theodore Roosevelt
Author of:
SQL Server Execution Plans
SQL Server Query Performance Tuning