That’s the only thing that can strengthen your problem-solving skills.
Search for coding challenges on Google , start with the easier ones.
ProjectEuler might be a good place to start.
Try Codeforces, questions there are rated by their difficulty level, overall it’s very sophisticated.
Note - It’s a competitive coding site, but it’s a sureshot at improving your problem-solving skills.
Any further queries are welcome!
I heard the book Introduction to Algorithms, 3Ed. (International Edition) (The MIT Press) is good very good.
It’s a great book but I won’t personally recommend this book for a beginner.
It’s too theoretical. It can be taken as a refernce book though.
My personal recommendation would be :
“Data Structures and Algorithms Made Easy: Data Structures and Algorithmic Puzzles” by Narasimha Karumanchi
(It contains some typos, beware of them. Otherwise it’s a good book)
I have this book at home but actually I didn’t the explanations good for beginners…