Apex Code Best Practices:

Best Practice #1: Bulkify your Code
Best Practice #2: Avoid SOQL Queries inside FOR Loops
Best Practice #3: Bulkify your Helper Methods
Best Practice #4: Using Collections, Streamlining Queries, and Efficient For Loops
Best Practice #5: Streamlining Multiple Triggers on the Same Object
Best Practice #6: Querying Large Data Sets
Best Practice #7: Use of the Limits Apex Methods to Avoid Hitting Governor Limits
Best Practice #8: Use @future appropriately
Best Practice #9: Writing Test Methods to Verify Large Datasets 
Best Practices #10: Avoid Hardcoding IDs