Many of my clients want to improve their credit. The best things to do: (1) pay your debts on time; (2) use credit only when necessary, and only have a small number of credit cards; (3) use only a small percentage of your available credit. The credit scoring systems look at your "utilization ratio" to try to tell if you are using credit responsibly, or if you are "maxed out" (4) check your credit reports at least annually for free at https://annualcreditreport.com, which is the official website sponsored by the three major credit reporting agencies. Dispute inaccurate or obsolete information.
If you are currently "swamped" with debt, consider filing bankruptcy to get a fresh financial start. Your credit can recover quickly if you follow the above advice after the bankruptcy. I have clients whose credit score is over 650 after one year after bankruptcy, and 700+ after two years. You really can recover your credit after a bankruptcy, I've heard that from many of my past clients over the years.