For error in reasoning questions, I found it really helpful to do some outside reading on logical fallacies. Working through the 33 Common LSAT Flaws is also extremely helpful so that you have some idea of what you should be looking for.
As for general method/error of reasoning times, focus on fully understanding the stimulus before you approach any of the answer choices. Map out the premise(s) and the conclusion and try to determine how the author gets from P --> C. If you can outline in your own words the method used by the author or the flaw made in their reasoning, it becomes much easier to pick out the correct answer from the generally abstract answer choices.
And, as always, practice, practice, practice! The more questions you do, the better you will get at recognizing patterns and common methods/flaws of reasoning.
Hope this helps! Keep up the good work and please let us know if you have any further questions.
