Just visited for the first time. Best advice is hire a guide! We booked an Uber from our hotel in New Delhi to Agra. It was a four and a half hour drive and I would probably take the train next time as both the Uber driver and the 4 times as expensive driver we hired through the hotel for the return trip started dozing off. I am sure they work long hours, but it made for an intense ride and we would have prefered a relaxing train ride. We spent the night in Agra so we could be at the Taj Mahal first thing in the morning when it was cool and there were less people. Our guide had a lot of great information, handled the tipping for us, kept the solicitors at bay, and knew all the best photo spots to take our picture. I was thankful that we hired a guide and would tell all my friends and family to do the same.