Hi Msantaana,
you can read my book. It is focused on EBS 12.2. We have a seperate chapter named : "Chapter 13 - Oracle E-Business Suite 12.2 Performance Recommendations"
Here is the link:
https://www.amazon.com/Practical-Oracle-Business-Suite-Implementation/dp/1484214234Lots of things to do there...
The ares for the performance recommedations: 
EBS 12.2 Client-Side Performance Tuning
EBS 12.2 Middle Tier Performance Tuning 
EBS 12.2 Database Structure and Performance 
Inıtialization Parameters 
Tablespaces, Data Files, and Redolog Files 
EBS 12.2 SQL Access Paths 
EBS 12.2 Network Performance Tuning 
EBS 12.2 Tuning the Concurrent Processing 
Performance Recommendations for Reporting, Workflow, and Application Debug Profiles