What are the major problem areas that can degrade SQL Server performance?

Following are the major problem areas that can degrade SQL Server performance:

• Poor indexing/Bad indexing
• Inaccurate statistics
• Poor query design
• Poor execution plans
• Non-set-based operations, usually T-SQL cursors
• Poor database design
• Excessive blocking and deadlocks
• Excessive fragmentation
• Nonreusable execution plans
• Frequent recompilation of queries
• Improper use of cursors
• Improper configuration of the database log