Salesforce Apex development is a powerful skill for building custom logic, automation, and integrations on the Salesforce platform. However, writing efficient, scalable, and maintainable code in Apex requires a deep understanding of Salesforce's platform constraints, best practices, and specific nuances.

Five key best practices that every Salesforce developer needs to follow to ensure their Apex code is both performant and reliable.

1. Bulkify Your Code Bulkification is a critical concept in Salesforce development due to the platform’s governor limits, which restrict the number of operations your code can perform in a single execution context. In traditional programming environments, handling operations one record at a time is common; however, in Salesforce, that approach could quickly lead to failures when processing large datasets. The concept of bulkification ensures your Apex code can handle multiple records in a single transaction, avoiding these issues.

Why It Matters: Governor limits control how many SOQL queries, DML operations (like insert, update, delete), and other resource-heavy activities can be executed. For instance, a trigger processing 200 records in Salesforce without bulkification would exceed the limit on SOQL queries or DML operations, causing the transaction to fail. To avoid hitting these limits, you must bulkify your code so it processes all records together, rather than individually.

How to Bulkify Apex Code:

Use Collections: Whenever you query data or perform DML operations (insert, update, delete, etc.), use lists or maps instead of individual records. For example, instead of executing an update inside a loop, gather all records that need updating and perform the DML operation in bulk after the loop finishes.
Avoid SOQL and DML Inside Loops: Having a SOQL query or DML operation inside a loop will result in multiple queries or operations being executed per iteration, quickly hitting governor limits. Instead, retrieve all records outside the loop, store them in a collection, and process them in bulk.
Batch Apex: For large datasets, use Batch Apex to process records in manageable chunks. Batch Apex ensures that the processing stays within governor limits by dividing the operation into smaller transactions.
Properly bulkifying your code will help your application scale effectively and remain within Salesforce’s limits.

1. Use Efficient SOQL Queries Writing efficient SOQL (Salesforce Object Query Language) queries is fundamental to optimizing Apex performance. Poorly written queries can lead to performance bottlenecks, high resource consumption, and hitting governor limits, which can severely degrade the user experience.

Why It Matters: Governor limits restrict the number of SOQL queries that can be executed in a single transaction. An inefficient SOQL query that retrieves unnecessary data or one that retrieves too many records can easily exceed these limits. In addition, inefficient queries can slow down your code's execution and increase the likelihood of timeouts.

Best Practices for Efficient SOQL Queries:

Select Specific Fields: Avoid using SELECT * to retrieve all fields from an object. Instead, specify only the fields you need. Retrieving unnecessary fields consumes more memory and processing time.
Filter Data Carefully: Use WHERE clauses to filter the data you retrieve, ensuring that you're only working with relevant records. This can significantly reduce the number of records being processed.
Use Query Limits: Leverage the LIMIT keyword to retrieve only the number of records you need, rather than pulling in large datasets.
Indexing: Where possible, use indexed fields in your WHERE clauses to improve query performance. Custom indexes and the use of indexed standard fields (like RecordTypeId, Id, etc.) can help Salesforce process your queries faster.
Avoid Redundant Queries: Cache data when appropriate, rather than re-querying the same information repeatedly. Using custom settings, custom metadata, or static variables can help you avoid unnecessary queries.
Efficient SOQL queries ensure that your Apex code runs faster, consumes fewer resources, and stays within the governor limits.

1. Leverage Salesforce Security Features Security should always be top of mind when developing on Salesforce. One of the most common mistakes developers make is neglecting Salesforce's built-in security features, such as object-level, field-level, and record-level security. Ensuring that your Apex code respects these security settings is essential for protecting sensitive data and maintaining compliance with organizational policies.

Why It Matters: If your code doesn't respect Salesforce’s security model, users could inadvertently gain access to sensitive data or be allowed to perform actions they shouldn’t be authorized to do. This can lead to data breaches, compliance violations, and overall lack of trust in the system.

How to Leverage Security Features:

Enforce Sharing Rules: Always use the WITH SHARING keyword in your Apex classes when appropriate. This ensures that your code respects the organization’s sharing rules and only allows users access to the records they have permission to view.
Respect Field-Level Security: Use the Security.stripInaccessible() method to remove fields from records that the current user is not authorized to see. This method can be used when querying, creating, updating, or retrieving records.
Object-Level Security: Before performing any DML operation, check that the user has the necessary permissions for the object and fields involved. You can use methods like Schema.sObjectType.Account.fields.Name.isAccessible() to verify access to specific fields.
By ensuring that your code respects Salesforce’s security settings, you help maintain data integrity and safeguard sensitive information.

1. Write Comprehensive Unit Tests Salesforce enforces a requirement of 75% test coverage for deploying Apex code into production, but achieving code coverage alone isn’t enough to guarantee quality. Writing meaningful and comprehensive unit tests is crucial for ensuring the stability and reliability of your code.

Why It Matters: Unit tests help identify bugs, performance issues, and incorrect logic before they reach production. They also serve as documentation for your code and facilitate ongoing maintenance by ensuring that changes to the codebase do not introduce new issues. Focusing solely on achieving coverage can lead to weak tests that don’t actually validate the behavior of the code, resulting in a false sense of security.

Best Practices for Unit Testing:

Test for Different Scenarios: Write unit tests that cover positive, negative, and edge case scenarios. Test how your code behaves when it processes expected data, incorrect data, no data, and when it handles maximum limit scenarios.
Use Mock Data: Salesforce recommends using test data generated within the test class to ensure the tests are self-contained. Avoid relying on existing org data, as it can change over time and result in inconsistent test results.
Test for Bulk Operations: When testing triggers, ensure that your tests account for bulk operations and validate the behavior of your code when handling multiple records at once.
Utilize TestSetup Annotation: Use the @TestSetup annotation to create common test data that can be reused across multiple test methods. This ensures consistency and reduces the time spent setting up data for each individual test.
Comprehensive tests make your code more reliable and reduce the likelihood of bugs making it into production, thus improving the overall quality of your Salesforce applications.

1. Implement Apex Design Patterns Design patterns are a key to building scalable and maintainable Apex applications. These patterns offer proven solutions to common software design problems and ensure that your code is organized, reusable, and easy to understand.

Why It Matters: Without adhering to design patterns, Apex codebases can quickly become unmanageable as the application grows. By following well-established design patterns, developers can write code that is modular, easier to debug, and more straightforward to extend.

Common Apex Design Patterns:

Singleton Pattern: Useful when you need to ensure that a particular object is instantiated only once within a transaction.
Service Layer Pattern: Helps separate business logic from DML operations, making your code cleaner and easier to maintain. It allows for better reusability of business logic across different parts of the system.
Factory Pattern: Used to instantiate different types of objects based on specific criteria at runtime. This pattern can help reduce complexity when you need to create various objects with similar behavior.
Strategy Pattern: Allows you to select an algorithm at runtime. This is especially useful when dealing with varying business rules or behaviors that need to be easily interchangeable.
Implementing design patterns makes your code more modular and easier to test, debug, and maintain in the long run.

Conclusion
Apex development on Salesforce requires careful attention to best practices to ensure performance, scalability, security, and maintainability. Bulkifying your code, writing efficient SOQL queries, leveraging Salesforce’s security model, writing comprehensive unit tests, and implementing design patterns will help you build reliable, high-quality applications on the Salesforce platform. By adhering to these practices, you ensure that your Apex solutions are robust, efficient, and future-proof.