It would be a good idea to meet up with fellow travellers where you might be staying, touring Delhi alone can mean you get ripped off everywhere. The main things to do are:
a) Dont get drunk in a public place. I'd avoid going to a nightclub alone altogether, but if you really want to go just make sure you dont get too drunk.
b) Agree on a fixed price with taxis when you are travelling long distances(such as to/from the airport). Taxi drivers will often try to fleece you and keep going for hours in circles(this happens to us Delhites too
) so its best to get a fixed price.
c) Whenever possible, use the Metro instead of buses(especially at peak hours), its much safer. Plan your trip so that places you want to see within a certain area are all covered together, since distances are huge in Delhi and rush hour is even worse.
d) Wikitravel has a list of sights as well as some general info, so do look it up. LonelyPlanet might have a list of good places to stay, so you should give that a shot too.
e) In INR, you will get ripped off though if you buy from malls and stores, you will probably only pay the MRP. The downside to buying from malls and stores is its not as much fun and you will get a lot less things that are unique to India. The Rupee being 1/80th of the pound however means that you wont pay much in pounds, at worst it will probably be the same overall price it would in Britain.
Dont just limit yourself to Delhi, if you find the time there are a lot of interesting places outside it too. Agra's 3 hours away while Mathura and Jaipur arent too far away either. I'm sure you'll have a lot of fun there.