You need to focus on your weakest section first. Try that for 5-7 days before moving on to your next weakest section.
Learn the concepts first then do some practice questions. I'd recommend using some
free question resources that also provide commentary on what questions are right vs wrong.
If you're weak in reading passages, try these set of
RC preview videos and see if they work for you.
The most important thing is to create a plan and stay motivated. You can do this by setting a deadline, telling your friends that you're taking the GMAT (forcing you to stick to your plan) and fitting in the time each day to go over concepts and then review time-saving strategies so you can finish the exam. If you're not finishing the exam, you need to focus on 1 key strategy -- reading the question/passage WITHOUT reading every word. This means knowing what to read and what not to read. Transitive words are important in RC. Scanning answer choices is important for SC. Try to find a video-based solution to show you exactly how to do this.