Could someone suggest a good book for elementary QFT and particle physics?(I dont know which to read first). I have very little idea about QFT. Could someone also tell me what maths knowledge is required?
I would suggest In order: Griffiths, Introduction to Elementary Particle Physics Then: Aitchison and Hey, Gauge Theories in Particle Physics Then: Maggiore, A Modern Introduction to Quantum Field Theory. Then the more well-known books by Zee, Peskin and Schroeder, Ryder, etc. As for maths, you need calculus in the complex plane, differential equations (Green's functions in particular), linear algebra, you need to know about the Dirac delta function. You don't need very advanced maths, actually.
I think Peskin and Schroder is brilliant. You'll also need Fourier transforms before you start, and concurrently learning some group theory is helpful. P&S is a good place to start with group theory as well.
It's better to learn it as you go, while doing QFT and particle physics. The books I mentioned introduce a bit of group theory, as much as you need to see the applications in particle physics. You could pick up math books on group theory but you would then have to learn a lot of stuff not used in particle physics before getting to what is required so it's not the nest way to do it (If you do use math books, make sure that you focus on the sections on Lie algebras). It's true that Fourier transforms are important. As for Peskin and Schroeder, I think that some part of it are good but some are confusing. Oh, I forgot: an ever better QFT book after you will have gone through the ones I mentioned is the book by Srednicki