There must be some queries in your stored procedure performing some inserts,selects,updates etc.
Check whether the strategic columns(columns upon which the above operations are taking place) are involved in some indexes or not.
If not, then create indexes involving these columns, it will help in minimizing the execution time of ur sp.
Next you can view the actual execution plan of ur queries in ur sp by clicking 'Ctrl+M', and then u can analyse where you need attention.
Google for some SQL tuning stuffs, and you can get help from them too.
Also, if ur sp has manier temporary tables, try to eliminate them by some combination and stuffs.
It too will help.
have a look at the below link too.
SQL Tuning Tutorial - Understanding a Database Execution Plan (1)