How to avoid slow process when data is huge in sql

Hi All,

I have a database In this there are multiple tables with reference. i have 50 lacs data in 3 tables now when i perform any operation like any update or reporting from the application.
many times i got Timeout error. Now i have to make an application for data archiving.
Through this application I want to move unneccesary data from these table through a small apps or scheduler.

Please give me suggestion to make this apps.Its urgent .

Thanks in advance