Here’s a great site — Common Errors in English — with an accompanying book by the same title. It is great; covers all of the biggies that drive me up a wall, like the oh-so common I/me gaffe, there/they’re/their, it/it’s, and a lot/alot more!
But the thing that really made me sit up and pay attention is that they included the MAC/Mac thing that so very many people screw up and drives me so very crazy.
So very helpful. Definitely something I will use and recommend.