You could google "improve sql server performance", and gave in awe at the prospect of weeding through over 4.6 MILLION results. Among them, you will find this one:
http://msdn.microsoft.com/en-us/library/ff647793.aspx[
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And just in case your question was actually about .Net applications in relation to sql servers, you will even find a several applicable items on that page under "Related Links".