Following the 2007-2008 implosion of the housing market, banks saw mortgage borrowers defaulting at higher rates than ever before. In addition to higher mortgage default rates, the market downturn led to higher default rates across all types of consumer loans. To maintain profitability banks began tightening lending practices. More stringent lending standards made it tough for anyone with poor credit to get a loan at a reasonable rate. Although banks have loosened lending somewhat in the last two years, people with subprime credit will continue to struggle to get loans. In June 2017, banks rejected 81.4% of all credit applications from people with Equifax Risk Scores below 680. By contrast, banks rejected 9.11% of credit applications from those with credit scores above 760.22
If you have a high balance on a credit card and are only making minimum payments, start paying down the balance. It's important to pay down (or even better, pay off) revolving accounts such as credit cards. This will lower your credit-to-debt ratio (what you have borrowed in relation to what you could borrow), and is one way to improve your credit score. Paying off installment loans such as auto loans, student loans, etc. won't improve your credit score as dramatically.
Next, estimate your monthly spending habits for other expenses such as gas, groceries and entertainment. Create a limit, based on your income, of what you can spend in each of the different categories of expenses. For example, if you tend to spend $400 a month on groceries, try to stick to $300 a month on groceries by making changes like buying generic brands, using coupons, and resisting impulse purchases.