How to avoid Error: "Too many SOQL queries: 101"

To avoid Error: "Too many SOQL queries: 101"

• Avoid SOQL queries that are inside FOR loops.
  
• Make sure you don't have a recursive loop calling a SOQL.
  
• Do not do any DML/CRUD inside a for loop.
  

Avoid more than one DML on a single object in a single transaction - because each DML invokes triggers of related objects can cause addition of SOQL count.

Avoid too many field updates in process builders in different conditional branches. Each branch runs a DML and initiates trigger execution.

If there are a lot of business processes and logic in your trigger then design and isolate processes with help of future and batch if needed.

Recursion Handling - To ensure a trigger is not running recursively.

Minimize the No.of SOQLs by merging the queries - we will merge the SQL query of a single object in a single query if possible. For Example:

Opportunity op = [select StageName, Account.OwnerId From Opportunity where id: opId];
List olis = [select id, productId from OpportunityLineItem where OpportunityId =: op.Id];
Change it to:
Opportunity op = [select StageName, Account.OwnerId, (select id, productId from OpportunityLineItems) From Opportunity where id: opId];