I am looking for book recommendations that will teach me the art of problem solving.
Learning theory is one thing but doing problems in limited time in a test is another.
To increase these skills I am looking for a book that has hard problems of high school level (i.e. pre college level) or maybe undergrad level which will teach me how I should approach a problem / solve it.{From Algebra, Calculus, Coordinate Geometry mainly}[Any books which give extra knowledge of some well known/important theorems , that are a bit above highschool level but not too beyond and can help in problem solving will also be really helpful :)]
Donald J. Newman’s A Problem Seminar is a classic and a delight, and you will certainly benefit from it. It is not a textbook, because it does not teach advanced theorems - it is specifically intended to get your mind aligned to problem-solving.
It has a hundred problems (two or three lines long at the most), then a section with a brief hint as to how to approach each one; and finally the main body of the book gives the answer to each.
The main thing about problem-solving as a specific skill is that it is a question of recognition rather than heavy lifting. The tools in Newman’s book are all within the reach of a high school mathematician. The reason the book is a challenging exercise even for university students is that knowing which tool to use, the key to all advanced mathematics, is a subtle and elusive skill, hard to learn, you might say impossible to teach. But it is a delight.
The book is rather expensive, new, and you might have to sell your grandmother to buy it. But you may be able to find a second-hand copy more reasonably: it came out in 1983.