ronit1894,
I scored a 620 on my first practice so I know how your feeling. After that I took a more strategic approach to my studying.
For the verbal section I spent a lot of time practicing active reading, asking myself questions and answering them as a read. I read a lot of passages and answered questions, but I also spent a lot of time reading things outside of GMAT prep books and software. The subjects in both CR and RC vary and if you aren't comfortable reading the subject matter a passage that some would consider easy could prove to be difficult for you. This is the reasoning for working through as many passages as you can. You'll find what you are comfortable with and can make more effort reading subjects that may elude you. For CR, I always thought of these small passages as abbreviated RC passages. You have to retain the information and usually have to make some inference, just as you have to do for RC.
As far as sentence correction goes, reading certainly helps there, but knowing sentence structure is the real key. There are a handful of errors that given sentences on the GMAT will have, all of these will be a violation of proper sentence structure. Some errors are easy to find, such as subject-verb agreement, but other's may be difficult to find. Also, errors can be buried in rather long sentences. Another key to this is knowing the structure of the answers, A - nothing wrong with the sentence, B- small error in sentence, etc.
Focusing on what answers are possible for questions is the key to doing well on the verbal section. This is also the benefit of being an active reader and knowing sentence structure. With these skills you can answer questions even before you read them.
For the quantitative section I feel like seeing as many problems as possible is the key here. When you get a question right, make sure it is for the right reason, and when you get a question wrong make sure you understand how you were wrong and how to correct your mistake. This advice also goes for the verbal section. I'm an engineer and didn't have too much of a problem with the difficulty of the questions asked, but I had to learn to take the most efficient route to finding the right answer. This came for the quantity of questions that I worked through and thoroughly reviewing my answers and the books answers. Again this applies to the verbal section.
When actually taking the GMAT timing can make or break you. If you work efficiently you stay relaxed. If you work inefficiently you will panic, make errors and either not finish a section or guess on multiple questions. Once you have some semblance of confidence in you ability to answer questions correctly, then it is the time to answer them quickly. You should time yourself and try to keep answering questions to under 2 minutes (usually). RC is different because you have to read a passage. For RC try to read the passage in about 4 minutes and answer questions in under 1 minute. If you've read the passage will this won't be too difficult, and you can even make up time. Again seeing as many practice questions as possible puts you at ease and won't leave any surprises when it comes to test time.
I self studied from a 620 to a 710 while studying primarily on my commute to and from work and a little on the weekends. I don't plan to retake the GMAT because I had a limited amount of time to study for the first test and got a pretty decent score, better than many people. But the key for me is I studied with purpose and didn't frivolously answer questions without investigating afterward as to why my answer was right or wrong. And I didn't give myself all the time in the world to figure things out.
Lastly, don't sweat it. You'll get to the point where you feel as though you have studied enough. Great. Take your foot off the gas and start reviewing your previous work. There's no sense in going into the GMAT overworked.
I hope that helps a little. Best of luck!
AustinLM