Folks get misdirected by the word "indulgence" which seems to mean something naughty.
Translated into evangenglish: An indulgence is a blessing that comes from God that has a powerful effect upon the person who recieves it.
To get this blessing the person must want to be closer to God and do something that brings Him closer, such as reading and meditating on the Scriptures or saying the Lord's prayer with devotion.
It is impossible to buy or trade these blessings as they come from God.
These blessings from God will not make up for unrepented sins. They will not spare you hell if you haven't surrendered to the Lordship of Christ. They will not earn you a higher level of heaven. They will help to bring you closer to the Lord and make you more like Him.
There is a little book that contains recommendations of proven things you can do to be closer to Christ in your walk with Him. This little book contains such ideas as:
+Memorize verses of Scripture and call them to mind throughout the day while doing your daily work
+Fast from something good and pleasing with a spirit of rejection of sin
+Devote yourself to compassionate service to those in need
+Teach or study Christian doctrine
+Begin your day with prayer
+Go on a retreat
+Spend time talking with the Lord
+Go hear a preacher or a mission
+Go to a brief mini-retreat each month
+Spend at least a half hour reading the Scriptures
+Recall your day and pray each night before bed
+Renew your baptismal promises
The book also has many recommended prayers for many different circumstances.
This book is called The Handbook of Indulgences (Enchiridion Indulgentiarum) published by the Catholic Church.