Hello Venkat,
Check out the link below. It is very useful for starters.
http://wiki.sdn.sap.com/wiki/display/BOBJ/Dashboards+(Xcelsius)+General+Best+Practices
You can find sample dashboards and XLF files in the links below.
Sample Dashboards:
http://www.sapdashboardgallery.com/
http://www.sdn.sap.com/irj/boc/xcelsius-samples