sql query optimization

my query is taking some 2029 msec to execute and my client requirment is it must be atleast reduced to 30% , i had created the indexes on the coloumns in the where clauses, and passed parameters to the coloumns and tried but still the performance didnt improved can u please suggest me how can i proced to improve the performance and to reduce the query execution time? and the application is a java application running on a linux server