Are you secretly (or openly) a member of the "grammar police"? Are you one of those people who feel a compulsion to correct misplaced apostrophe's [sic] or to remove excess commas? The Wikipedia Typo Team is for you!
If you are the least bit nervous about editing or authoring a Wikipedia article & you're good with the mechanics of English, correcting these minor (& some not-so-minor) errors is a useful, low-threshold way to start contributing. The Typo Team is "dedicated to improving the quality of Wikipedia by correcting typos and misspellings." The team info page (linked above) lists a number of lists in which you can find pages that desperately need your help. Since pages with multiple misspellings often include mistakes with grammar & punctuation as well, you can have a heyday.
As a member of the Typo Team, you get to add a userbox to your userpage.
You can even "adopt-a-typo" and become the caretaker of a specific typo. So fun!