Just some 'tips' won't work when come to database implementation. You should know everything from Oracle, System, OS to application. Otherwise you will be creating bottlenecks in one or other place. I saw one application which was working faster in a normal PC but failed to achieve the same performnace in a high end server (interestingly the server was installed by the Vendor, one of the global gaint the market!) just because of RAID-5 and lower RAID Controller memory along with smaller stripe size.

So, "I don't know " will lead to another round of end user performance complaints. Grab DBAs / Application Architects/ SYS Admin and discuss with them. Good luck.