There is a system that banks have started using to determine if you are worth investing in. Yes, you are an investment to the bank, you are not a person in their eyes.
This is one of the many atrocious systems that develop in capitalism, and here's how to easily improve that score. Now this will only work if you can also avoid any criminal charges from here on out, a criminal charge that you cannot pay the fine on will reset all your work, which is why there are many crimes which they only enforce on the poor.
So the first step is to get a checking account, specifically a checking account with a debit card. Most banks are required to have a low income account, they often give them a name similar to "starter" account.
When you use this account, use the debit card more than checks, if you can just do the debit card. Use it like a credit card when possible as well, just be sure to never go over your balance.
This is the hardest part because we all need money sometimes and that temptation will be a struggle for most people. I know because I made the mistake a few times before I managed to finally resist that urge.
I was living in shelters at the time so it didn't impact me nearly as much. Now if you do live in a shelter you will need to get housing to accomplish this, so get on those lists and use the time while living in the shelter or on the street as practice.
After a few years the bank will start giving you offers for a deposit backed credit card. I didn't say this was a quick method, for us poor people there is no quick method.
Once you get these offers, not how much you need to deposit and try to save enough that you can afford that deposit. Don't worry about your needs being covered because you will be using the credit card for all of that.
Yeah, you have to go into debt for this to work and that may be scary, think of it this way: you're using the deposit and then loaning it back to the bank the next month. With this card you can't go over the deposit, and you will get that money back at the end, so you are not truly in debt now.
Your credit score will see a small increase from this, but nothing big until the next phase. Once that test period is up, as long as you kept paying it off every month, you get the deposit back
By now you'll be used to not over spending, and paying it off every month means you don't get hit with a ton of interest. Keep doing that, use the credit card for all your purchases during the month and pay it off with your paycheck every month, do not spend more than what's in your checking account.
If you feel comfortable, buy something large once in a while, worth no more than twice your paycheck. Then spend a bit less on regular things so you get that large purchase paid off in a couple months.
After no more than 5 years your score will be at least 700, after a decade you will have a score of 800. That last 50 is much more difficult, because the score itself is influenced most by how much credit the bank trusts you with.
So yes, every time they offer to increase your credit limit you say yes. But never ask the bank to increase your credit limit, doing that will decrease your credit score and you won't get an increase, wait for them to do it for you.
This happens for wealthy people automatically, because they get credit cards from their parents, jobs, or they deposit a large amount of money and the bank gives them one for that. But if we all get 800+ credit scores we ruin their system, we crash the credit score.