you should find a good verbal course and practice alot.
for RC by reading alot to improve you RC skills , I wasn't struggling much with it because I already read alot of scientific material in English because of my job requirements.
But I was struggling with SC, I tried both
E-GMAT and
TTP, I found that
TTP SC section more organized, comprehensive and realistic, they provide detailed explanation for each Question answer and why it is correct and why it is not, and that Explanation is what helped me understand why I keep making mistakes in SC questions, and how to analyse each part of the sentence and determine whether it is correct. so bit by bit I started to realize how to approach SC questions, analyse the sentences, and answer the questions. after finishing their SC section I realized how much I was missing. with
E-GMAT things were not as organized and clear as with
TTP, so I felt lost and frustrated with
E-GMAT.
for CR I haven't yet started.\
Anyway
TTP has a 5-day trial for 1$ so you can try and decide yourself.