Hey Neha, In Agra visit Agra fort and Taj mahal. Then you can go to Fatehpur Sikri (35KM from Agra). Visit Buland Darwaza,Tomb of Salim Chisthi and Panch Mahal in Fatehpur sikri. Hope this would help you.
Visit redBus.com you'll find a Agra sightseeing tour packages for a single day. it'll cover tajmahal, Red fort, Gokul, Mathura and Vrindavan. fare is normally around? 600 for 2x2 luxury coach. it will depart from different points through Delhi from 5-30 a.m. takes five hours to reach Agra and in evening leave from Agra at seven or eight and drop you in Delhi at your point after or around one or two midnight.
Simple start early in the morning from delhi . its about three hours drive by road. visit taj mahal and have lunch by afternoon. visit rose garden and by evening catch a bus back to delhi. make sure that its not friday beacuse taj mahal will be closed on that day for tourists