A few things. Keep in mind that a 500 is actually not that bad - we've seen people here with 300's, and even some in the 200 range I think. So first off, be happy that you at least have a good springboard from which to start!
1. You can get to 700 from 500, people have done it, so don't despair!
2. The bad news: A 200 point jump is going to require a signficant amount of effort on your part. How much time do you have? From what I've seen, most people here (who get up to 700's or near there) study about 2 or 3 months, and usually push well over the 100 hour mark. For sake of comparison, I went from 600 to 730, with something around 250-300 hours of work, including almost 15 practice exams. In short, if you really want the 700, you can get it, just be prepared to roll up your sleeves. The good news: Some other people have pulled 700's with far less studies than myself. Everything from (honestly) - studying on a train on the way to the exam the day of, to a month or two of studying. You probably wont be able to do it with one day of studying obviously, but you may not be facing 300 hours either - especially if you already got a 620 once.
3. You didn't mention the Official Guide - this was a critical mistake. This is the only book out there that, no matter who you ask, is absolutely worth every penny. All other books might be good, or great, depending on who you ask, but this book is the engine in your car. Without it, you'll never get out of 1st gear. Buy this today.
4. Other possible resources: The official guide supplements - there is a math one and a verbal one. These are not necessary, but if you have a long study schedule in front of you, the extra problems might be helpful
5. Did you take practice exams? If not, this was also a key factor. If you did, what did you score? Did you take them with the essays? (If no to either, when you do take them, make sure you do the essays too. The GMAT is a test of endurance more than anything else)
6. Manhattan GMAT books
- there are 7 of these. They are all great in my mind - they do NOT include questions, they simply re-teach you material from the ground up. Rather than teach you a tip or a trick to solve some kind of problem, they teach you how to solve the problem, THEN show you a faster way. Their view is that, if you don't understand the fundamentals, tips and tricks wont get you anywhere. If you are like me - and can't remember how to solve geometry problems, or find yourself suddenly weak in basic algebra, these books are amazingly helpful. I think of it this way - first, you need to learn "Algebra", then you need to learn "GMAT Algebra". If you only buy one of these books, there is no question which is the one to buy: The Sentence Correction book. Everyone swears by it, and with good reason - many people have seen their verbal scores go up a lot after getting through it. I personally took my scores from 35-38 to 44-45 with Manhattan SC. Thats a huge jump, and you might not get that much out of it, but for most people, this is a great book. It looks like you need to work on both math and verbal, so I'd personally suggest all of these books. If you can afford it, Manhattan courses were also excellent in my view - I only had 4 people in my class. Some others have said they had a lot more and were less happy - so your mileage may vary. I don't doubt that, without Manhattan, I could never have pulled a 700+ score. Avoid Kaplan
courses at all costs.
7. Create an error log
and review it. Every question you get wrong, write it down. There is no right or wrong way to do this - in a notebook, word, excel, whatever works for you. The point is, force yourself to go back to every question you got wrong and re-review it. Don't just look at the answer and say "Oh I see" - you don't see, that's why you got it wrong - force yourself to really understand why again and again until you stop getting those kinds of questions wrong. Honestly, I think an error log
can make the difference between a mid 600 score and a 700+ score. Don't underestimate the importance of this step.
8. Make a schedule you can stick to. Better to do 1 hour a day every day than try to "catch up" on Saturday. I can't tell you what schedule to follow because, everyone's life is different. What I can say is this - Pick a schedule that is REASONABLE and REALISTIC. I've seen people come in here listing every GMAT book ever written in the last 20 years and laying out some 50 hour week schedules that run for months claiming they are going to do everything in every book twice. They won't - a week into it, they'll burn out. So, if you think you can handle 1 hour a day and maybe 3-4 on saturday and sunday, try that to start. If that works well, try 2 hours a day and 5 or 6 on saturday and sunday. You just need to find what works for you. The issue is not the schedule per se - the issue is finding one you'll actually do.