SQL Query optimization techniques

Queries optimization in SQL SERVER

Use between clause in place of  Comparisons like <= and >=

When comparing dates like <='2001-02-02' and >='2014-01-03' we can simply use filter like date between '2001-02-02'  and '2014-01-03'.

Don't club sub queries when using union operation directly.

Store the results of each sub query in a separate table then apply union operations on that.

Try to reduce functions in Queries.