Hello,
If you are wanting to boost your credit you may want to do these three things:
1. Fix negative credit
2. Create paths for good credit
3. Maintain good credit habits and remove the negative
1 - You want to get rid of collections or inquiries that will damage your credit score. You can dispute most of these online or by mail. Even if a collection is righteously owed you may be able to get a removal if they do not respond in a timely matter. Optionally, a credit repair service can do this for you.
2 - You need some positive credit being reported on you. Look into secured credit cards, shared loans or secured loans.
3 - You must create good habits. Pay all bills on time and never be late. Limit how many times you apply for credit to avoid a large amount of inquires that will hurt your credit score. If you get a credit card, secured or not, be sure to pay it off in full each month. I highly advise you to not go into any debt on a card that can't be paid off the next billing cycle. Keep your card utilization under 30 percent. This means only carry a balance of $300 on a $1,000 card. Lastly, always enable auto pay if it is offered.