Reddit reviews Woe is I: The Grammarphobe's Guide to Better English in Plain English, 3rd Edition

The Oatmeal, an online comic, has tons of hilarious and snarky posts about grammar.

Grammar Girl's quick and dirty tips is fun, but it's more topical than comprehensive. She also has a podcast that might be more interesting than just reading something.

That said, /u/meggawat recommended some great fun books that are easy reads.

I'm also fan of Woe Is I by Patricia O'Conner.

An important thing to keep in mind as you approach this vast and exciting grammar excursion: there is no universal, all-correct grammar. Grammar is socially constructed and often varies from user to user, from style guide to style guide and from one context (writing online to a casual audience) to another (writing a formal cover letter for a job application). Don't get too hung up on your "weak grammar." Words are for using and expression. Sure, grammar can afford some clarity, but even as I make my living off of its "correct" (or consistent) use, I question the prominence we place on "strong" grammar.

TL;DR: Have fun, but don't get too daunted by the details.

Woe Is I is a great one. I use it all the time when I'm preparing for class.

The books Grammar Girl's Quick and Dirty Guide to Better Writing and Woe Is I helped me learn the parts of speech. They both break things down pretty simply and are easy to follow. Both use lots of examples, which I found helpful!

*Yes, you are right. What do I need to do to improve it?

Here are several links to books that might be helpful:
Link 1
Link 2
Link 3

Here are a few grammar books that are not only helpful but also very readable. Actually, a quick Amazon search brings up a lot of books, but these are the ones I recommend from firsthand experience:

Eats, Shoots and Leaves

Woe is I

Grammar Snobs are Great Big Meanies (<-- probably the most informal of the 3)