I always love to take print-outs of Cheat-Sheets (or) Quick Reference Docs and clip it to my board. When you learn ruby (or) rails, these Cheat-Sheets would be of great help in remembering the most commonly used syntax and TODO’s.
Here in this blog post,you can find some of the useful reference sheets,
If you find any useful Rails resources, do share them in the comment section.
Note: Cheat-Sheet will be getting older as new versions get released, So If you find any obsolete data, would suggest you to ignore them and follow the new once. Also most of the topics in the cheat-Sheets would be fundamentals and would hardly undergo changes.