A second hand car(if you can determine it is which hand it is one step is done) can make or break your peace of mind. I would not suggest someone who does not know much about cars to go and buy a second hand car because it can be traumatic experience. By second hand car buying I am referring to used car buying which can be of any hand.
The best deal is that you are buying from someone you know, and trust(which is a rare thing, and you will hardly get any deal like that) so that he is able to tell you mostly what is right and wrong about the car. But rarely you will get such deals.
Step one: Figure out your budget, and keep it flexible by 15 to 20% up and down. If you get something which is slightly above your budget but is a good deal, better take it, so you do not spend 10 times more the amount after buying the car.
Step two: Make a survey on the net, several sites give info on Indian car market geog basis - check out the models which are in your range, and decide on couple of models which you can go for. Also decide the mileage and the make which will satisfy your need. Come down to a small list of probables otherwise you might be lost.
Start search through all sources, word of mouth, news paper, net, brokers(if only you have a dependable one) etc. Keep one dependable person who knows about car readily available so he can do an inspection for you(assumption any one who is reading this article does not know much about cars). This opinion is very important because experts can give you good value.
Mileage and single owner, self driven are the attributes one should look for. Also try to find out why the owner is trying to sell the car, here a known seller is better.
Check the papers properly and see that all the papers are completed before you start discussing the price. while you are doing a prelims you will have an idea of the price, and based on that start your negotiations. If you feel that the machine is good, and the owner is genuine, and the things he is saying is true be ready to pay slightly more. While evaluating a second hand car, also look at the fittings which are available, because these should be kept in mind while negotiating. The car should not have any accident history etc.
Take it to an expert(who does not have any personal interest in the deal, positive or negative, and who you believe will give you an unbiased opinion, maybe for a price) who will evaluate if you are not an expert, before you sign the check.
ALL THE BEST, and I hope you have a GOOD DEAL, this is in very brief.