My 5 cents:
One good thing is: C# is low in bad legacy. It's much better for a starter than C++ (now C++ fans will throw stones at me, but I'll tell: one of the most destructive factors indirectly slowing down development of software technologies; don't worry: I know it pretty well to judge (I can imagine how many down-votes it may invite :-))) and many other things.
That said: one important thing is to focus on fundamentals. Learn theory and fundamentals more than concrete APIs or even language. Try to see ideas behind syntax. How about your mathematics, by the way? Got an idea on elementary set theory, theory of numbers? Many of such topic could be learned well in a week, if you develop the skill to read mathematics texts well.
[EDIT]
Alireza Oliya asked:
…do you know a good book that has discussed about this or is it a figure for myself?
A while ago, I gave somewhat paradoxical advice:
As to the books… You know, decent creative engineers and people going in for other creative fields of activity don't ask much for recommendation for the books (but of course take recommendations into account when such recommendation comes). Such people pose the problems, try to solve those problems and, as some part of it, try to find the answers in the work or other people. And then the books, figuratively speaking, comes to such people by themselves.
But don't get me wrong: the books are very important. But you need the books to learn the fundamentals: theory, mathematics, ideas, methodical approaches, first principles. To learn some particular computing systems, libraries and other application stuff won't require any books; just reading the original documentation and practicing development would work for you much better; these days, some on-line manuals, especially original ones, are nearly perfect for everyday work.
In fact, I just admit my inability to give you any particular advice on any particular books, sorry. At the same time, this matter can be very individual. There are many different ways to get some education, I just don't know which is the best, and maybe this is not the main thing. The important part is: it should be real, not illusory.
—SA