Hi vatsalcby.
You need to identify the areas you need to work on and then work on them one at a time.
You can identify the areas you need to work on by analyzing your practice sets and practice tests to see what types of questions you missed or had trouble with. Also, you can simply consider what types of questions you'd rather not see when you take the GMAT.
Once you've determined what topics you need to work on, work on them one at a time by
- first, reviewing the relevant concepts and strategies
- then, doing practice questions involving that topic UNTIMED until you're achieving high accuracy
- finally, working on reducing the time per question until you're correctly answering questions involving that topic at test pace
Your issues with speed will be addressed by your strengthening your skills in your weaker areas.
For more insights into how best to practice for the GMAT, see this post.
The Best GMAT Practice Methods