(Note: Provide or distribute PDFs only in accordance with copyright law.)

Do not look at the solution first. Cover the right side of the PDF (or hide the answer pane). Attempt the problem with a pencil and paper for at least 15 minutes.

When you see a solved problem that asks "Prove that the center of a group is a subgroup," do not just read the proof. in your own words. Then try to prove "The center of a ring is a subring" without looking.