how can you optimize SOQL query to fetch data from Salesforce Database?

As Salesforce doesn’t save data in traditional way. Data of all tenants are in common table, so traditional Query
Use the Query Plan tool to optimise and speed up queries done over large numbers of records. View query plans for SOQL queries, SOSL searches, reports, and list views. If custom indexes are available for your organization, use query plans to help you decide when to request a custom index from Salesforce Support.

For more details visit here-https://help.salesforce.com/articleView?id=code_dev_console_tab_query_editor_query_plans.htm&type=5