I've been there a fair share of times. Probably be back sometime this year again.
Tips or advise? Let's see.
First off, do you intend on leaving the airport or not? (Serious Question)
You will find that the airport is more like a bus station in a poor rural town, don't go expecting LAX or JFK.
Depending on the day 10 hours might be just enough time for you to successfully transfer to and catch your connecting flight. (That's not a joke)
If you head outside the airport there are a few simple rules to follow.
Don't go far. Travel takes 5 times longer in India then in most other places I have ever been (Except maybe N. Africa)
Take a STACK of $1 bills. They will go far! Don't worry so much about Rupees, just give people a couple of ones (Well, maybe a few now with the dollar where it is) and watch their face light up.
EVERYONE is a con man. Let me repeat, EVERYONE is a con man. Sounds cynical I know, but after you have spent some time there you will understand. As a foreigner you will be accosted the minute you step foot outside the terminal from everyone looking to handle your bag, to getting you a cab, to giving you a tour. Ask how much everything is up front. Indians love to haggle (I know, I married one

) and you can't go into a shop and buy so much as a pack of batteries without some sort of back and forth haggling, just be ready for it.
Don't give money to baggers. Without going into great detail just do yourself the favor, trust me.
New Delhi has a few U.S. chains, so you might feel a tiny bit at home. I normally don't say anything like stay away from local food because it sound a bit xenophobically closed minded, but be careful what you eat. I would say stay from fish if you can, everyone I know (Including myself) has gotten into big trouble consuming fish in India outside of a western style 5 star hotel.
Grab a taxi into downtown, a taxi not a tut-tut (Again, trust me). You could get over to Red Fort and have a look around, nice place for some photos and video. The airport is only about 10 or so miles away, if memory serves me.
In case you didn't already know, going to the Tai Mahal is not a possibility. I have never made it from New Delhi to Agra in less the about 5 hours, one way!
I'll ask my wife for some my info when she gets home. She grew up there, I just go to visit family.
Good luck.
KD