English isn't my native tongue, but I've been writing novels in English for a while. Most of the time, I can be aware of what's grammatically correct and what's not. But making sure that a sentence sounds like one written by a native speaker is a harder task. 

I've been trying the following:

* Writing everyday (I try using simple words and simple sentences)
* Reading every day (and check in the dictionary words that I don't know)
* I copy paragraphs from my favorite novels (I read the paragraph once, I write it, and I correct the differences.) In the process, I check in the dictionary every word I don't know (or translate it to Spanish, my mother tongue).
* Writing everyday
* Check my sentences on Google Books (the more results the more confident I am. If there are zero results, then the sentence is probably wrong).

I'm not sure if these are the best ways of accomplishing what I want.
Any suggestions? (other than looking for a native speaker to correct my work)?