There are few points that we should have to care for improving the performance: 1) Database design and normalization. 2) Indexes 3) DB Statistics 4) Use EXISTS instead of IN because the former stops processing once it has found a match. 5) Avoid scalar subqueries in the SELECT-list. 6) Use joins instead of subqueries, as it gives the optimizer more room to play around in. 7) Avoid implicit conversions of data types, especially in the WHERE clause 8) Avoid, whenever possible, comparison operators such as <>, NOT IN, NOT EXISTS, and LIKE without a leading '%' for indexed columns in predicates. 9) Avoid DISTINCT unless you have to use it.

There could be several techniques for example. 1. HAVING OPTIMAL INDEXES: It means neither less nor more indexes should be there in a tables. for example fields used in where clauses should have non-clustered indexes etc. It should be evaluated properly before putting index and DB adviser tools can be used here as well. 2. RUNNING STAT REGULARLY: Running DB STATISTICS organizes the indexes for faster retrieval. I have personally experiences this. 3. RESOURCE (RAM/CPU): Keeping an eye on resource availability is equally important. Sometime due to resource bottleneck, DB runs slow.These were the suggestions that I can think of right now form my experiences. If this helps to address the issue, please close the thread by accepting the answer.

http://www.codeproject.com/Articles/35665/Top-steps-to-optimize-data-access-in-SQL-Serv

Normalization