Data Sufficiency

I am noticing that I am plugging in numbers for data sufficiency and overall quantitive section. This usually works if I pick smart numbers and if I choose and if I test FAR enough. The problem is sometimes I am not picking the right numbers and this yields a wrong answer. Also I am sometimes choosing the correct nubmers but not testing far enough this also yields a wrong answer. My take away from these questions is I am not being careful enough but is there anything else I can learn from these kinds of mistakes. Help help help.

I looked around for this type of topic but couldn't find it. apology in advance if one already exists!