What are the grammatical errors here?

The most effective and efficient way

> The best way

that you can improve your chess

> to improve your chess game

is to solve tactical puzzles by theme from a book.

> (no change)

As a beginner you must acquire the tactical pattern knowledge.

> As a beginner, you must acquire tactical pattern-solving skills.

You can do this by solving the same type of puzzles all over again.

> You do this by solving the same type of puzzle over and over again.

The problem with online tactics puzzles is they are random.

> The problem with tactics puzzles you find online is that they are random.

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The best way to improve your chess game is to solve tactical puzzles by theme from a book. As a beginner, you must acquire tactical pattern-solving skills. You do this by solving the same type of puzzle over and over again. The problem with tactics puzzles you find online is that they are random.

The problem with online tactics puzzles is they are random

=The problem with solving online tactics puzzles, is THE PUZZLES APPEAR are PRESENTED AT random

Although there is a difference, I think I would only use effective.

The most effective way to improve your chess is to solve themed tactical puzzles from a book. As a beginner you must acquire tactical pattern knowledge. You can do this by solving the same type of puzzles repeatedly; the problem with online tactic puzzles is that they are random.

Not sure they're really errors but I'd get rid of "the" in the second sentence, change "all over again" to "over and over again" and "online tactics puzzles" to "online tactical puzzles.

Not a grammar question but I don't see why online tactical puzzles being random is a problem.