This is easy to say, however in priority here are my thoughts
1. Attack the bad trade lines, either getting them removed or corrected. If you can't get them removed or corrected, it is unlikely you will see 800's until they fall off.
2. During working on item one above, establish 3 or more credit cards, 5 is ok, 3 is the sweet spot. PIF each month or carry low balances. This effects 65% of you score (Payment History and Amounts Owed).
3.Consider one installment loan if you don't already have one, this helps your (Credit Mix) at 10%. At 6 months to year of age should add 10 or more points to your score.
4. After or during establishing item two and three above, the next most significant item is (Credit History) 15%, if you have it, great. If not, it might be worth taking a look at AU or joint account if you have those options and want to take the risk. Some are against this on the board, however, it is a perfectly legal option. Execute at your own risk. I don't know the threshold, but I'm thinking you need around an AAoA of 5 years to reach the 800 mark with no baddies.
5. Next item to look at is New Credit at 10%, once you have the credit cards, instalment loan. Simply don't apply for credit unless you have too. Keep paying on time, focus on keeping low or no balances for at least a year, two is better. Time time will allow inquiries to drop increasing your score. The credit cards you have opened need to age for a couple of years.
If you have baddies and can get rid of them all, you should reach the 800 mark in two to three years provided your AAoA is around 5 years. just a questimate on my part.
If you can't get rid of the baddies, your in for a long ride, however once baddies dropped, you will be in a position to reach 800+
