Common Grammar and Usage errors:
3. Run-on Sentences (Fused & Comma Splice)
6. Lack of Subject-Verb Agreement
7. Confusing verb forms and tenses
8. Confusing pronoun case forms
9. Use of double negatives
11. Use of plague words and phrases
Answering Yahoo questions, I have noticed quite a lot of grammar and usage errors committed by people either with little English skill or someone with above average English ability.
I decided to start compiling some of the common grammar and usage errors. These are what I can think of for now. I will continue to add topics to the list as they pop up.
Some of these, I have described in details in my previous articles and you will see links to these articles. The ones without links are the ones I haven't written. As I write one, I will place the link then.