How do I clear my system Cache?

How about just booting in Safe Mode.

http://support.apple.com/kb/HT1564

Use to be that font cache and extension cache didn't get updated or deleted properly and when needed, but I think that is mostly in the past now.

A safe boot can be useful.

Applejack is still one of the tools that has never let me down, can't say the same for others.

Web browser caches do need to be 'pruned' and sometimes manual is best.

I think most would ask, "Why do you think you need to?"

To communicate with MacBook Pro owners, that forum is here:

https://discussions.apple.com/community/notebooks/macbook_pro

I am of the opinion that asking for "system running sluggish and slower" is

very common

more helpful

threads of others on the SL forum - every since 10.6 shipped in Sept 2009

and your fellow MBP owners might know better

Low memory, laptops use slower 5400 rpm drives, Safari seems to be a huge culprit on not releasing RAM or limiting the size of its web history and cache that grow too large.

Reboots, safe boot, even repairing permisisions and reboot, all seem to help. But they should not be needed!

Always a good idea to have bootable clone (backup) that you can work from, repair your main drive with, and so before you do make changes you have a fall back plan.