How to run SQL query in Oracle?

Could you please elaborate on the steps involved in executing an SQL query in an Oracle database environment? What are the prerequisites I need to have in place before I can run an SQL query? Also, could you guide me through the process of writing and executing a basic SELECT statement as an example, highlighting any potential pitfalls or best practices to keep in mind? Additionally, how can I ensure that my SQL queries are optimized for performance in Oracle?