How to improve our C# skills

IMHO, no pain more gain. The more challenging the path you travel, the more stronger you will become. Apart from solution 1, I would encourage you to participate in some coding forums, like Code Project, where you get to come face to face with all sorts of real coding questions. One sure way to tougher your skills and knowledge is by attempting to solve them, or simply learning from the experts' solutions, their advice on do's and dont's, exchange of discussions, and many links to good tutorials. Cheer!

Master some analyze methods, Dijkstra Top-Down method is a good start.
https://en.wikipedia.org/wiki/Top-down_and_bottom-up_design[^]
https://en.wikipedia.org/wiki/Structured_programming[^]
https://en.wikipedia.org/wiki/Edsger_W._Dijkstra[^]
https://www.cs.utexas.edu/users/EWD/ewd03xx/EWD316.PDF[^]

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You should learn to use the debugger as soon as possible. Rather than guessing what your code is doing, It is time to see your code executing and ensuring that it does what you expect.

There is no magic in the debugger, it don't find bugs, it just show you what your code is doing.

Debugger - Wikipedia, the free encyclopedia[^]
Mastering Debugging in Visual Studio 2010 - A Beginner's Guide[^]

There is no shortcut for it , you can practice Small example programs in the starting and try to automate many things using coding.. Reading and finding solutions to the challenges you face will give you expertise gradually..