There's so much more information needed before anyone here could start to help you. Starting with why you feel the need to tune the system in the first place.
If you honestly don't know where to start, I would suggest you find somebody to speak to that has experience of system tuning. A couple of days with an experienced NetWeaver consultant analysing the system and providing recommendations could save you a huge amount of grief compared to going it alone.
I notice you said "customer". Do you not have somebody in your organisation able to provide this support to them?
Steve.