This is always a tricky thing to get used to in any foreign country if you're not from one that does so, and that is the tipping. It can always be tough to work out how much is an appropriate amount, you don't want to over tip, but at the same time you don't want to risk insulting anyone!
I will start by saying this, it is YOUR money! You do not HAVE to tip anyone, it is entirely your choice how much you want to tip, and if at all.
Personally, I rarely tip living here. I do on occasion, but not with every purchase I make, or every shop/restaurant I visit. I will generally save it for situations I feel stand out to me. An amazing meal or terrific service for example, however I don't really see the need to tip simply on the basis that someone brought me the meal I am paying for as it is!
I do know people on the other hand who will always leave a tip for every meal at every restaurant. How much will always vary depending on the situation.
To start with I will say this, if you are a tourist and eating/shopping at touristy places, chances are:
A service charge will always be included in everything you buy. (Generally its 10%)
You will be paying a 'Tourist' price (Basically...they are charging you way more because they know they can!)
So if you want to be adding a tip on top of this also, that is entirely up to you, but I don't really think it is necessary.
To give a good indication, anywhere between 50-100 rupees is appropriate for the majority of purchases you will be making, restaurants etc. Any more than this is excessive in my opinion, but it is of course up to you.
If you have had a tour guide/driver for a week or so who you have found very helpful and feel has gone the extra mile for you, you may want to give a bit extra (When I was here holidaying we just gave our left over money to ours), but otherwise as stated before, I think no more than 100 rupees is suitable.