How To check bottlenecks in SAP

Hi Experts,

What are the parameters we need to monitor at the time of slow experience of the performance of the system , we are having two IBM power 4, AIX 6.1 , systems with Oracle 10.2.0.4 systems.

One is  System is central instance and another is application instance, and we are having 330 users in SAP.

Please suggest us.

Regards

Rj