In this guide, it will explain how to create a database instance and also the configuration for database listener. Later in the guide it will tell how to configure listener after instance creation. However, it is better if the listener created first. In initialization parameter, there are several parameters that I used to change such as:
cpu_count –change the value to 80% of total cpu (using mpstat)
cursor_sharing –change the value to SIMILAR or FORCE
open_cursors –change to the desired values
process –change to the desired values
sessions –change it to = (process*1.1) + 5
For character set it is preferable to use Unicode and leave others to default. To keep it short here is the document.