As an English speaker, there are things that I always have trouble getting my head around.

- Subjunctive: English speakers don't use this all that often so it takes work to use it correctly.

- Slang, Idiom and Casual Talk: While I would say I could read the average newspaper article without that much help, I still struggle with the day to day basic communication. My Spanish is very much school learned.

- Professional Vocabulary: I would say that the more formal vocabulary for talking about certain topics (politics, health, business, etc.) would be useful and I would assume it would be rather uniform from country to country.

I totally agree with the others. I would like a blog that featured more slang and idioms. 

Though it would be nice if you wrote about other interesting topics (apart from grammar, language learning, etc.). Maybe you could write non-fiction articles on a variety of subjects like: music, shows, travel, food and etc. Or write short conversational pieces in Spanish about Spanish in certain situations.

I just wanted to ask, are you writing a blog "about" Spanish in English? Or are you writing a blog in Spanish that also happens to be about learning Spanish? 

Personally, I feel that it has a lot of blogs discussing Spanish in English and would like to see more blogs written in Spanish. 

Hope this helps :)

I second the casual speech and slang idea! 

Make sure to share your specific country's/regional slang so that people know where you're from.