You can improve your credit score a little bit within 30 to 60 days.
But to really improve your credit score it can take from 3 years to 7 years to improve the credit score unless you hire a credit repair agency to help remove derogatory remarks from your credit score.
Negative remarks such as bankruptcy, late mortgage or late loan payments, Foreclosures or Short Sales take up to 7 years for the Negative Remarks to go away.
So while some people say you can really improve your credit score in 30 days, the truth of the matter is it takes years to recover from bad credit so don't expect quick results.
You can get a credit card that you put a deposit on and then use the credit card responsibly which can help improve your credit rating and credit score overtime.