Even if you are not a native writer, you can write a good SEO article. However, before explaining to you how is it possible to write better articles, let's talk a little about the market of articles, and about some methods that would allow you to position yourself better in this market.
There are some writers that can't even spell basic English, writers that are still able to make good internet money. How is that possible? In my opinion, every ORIGINAL article written on internet has its value. Even those written by Asian writers with no experience and skills have their value. Maybe a buyer would not be willing to pay more than 0.5 $ / 500 words of this kind, but even such an article can be sold by people who know how to write SEO articles.
You might ask what a person would do with such an article. I must admit I have never asked my clients what would they do with my articles, and this is one of the basics rules that you must respect when you write SEO articles. As long as a client has paid you for an article, you don't have any right about it anymore. In fact, this is the basic of content article writing, and this is the reason why this kind of writing is called ghostwriting.
However, I think there are two methods for buyers to use this kind of bad SEO article. First, they might use it only for SEO optimization. The article would be placed on an obscure page of their website, in a section that is never accessed by visitors, only for SEO purposes. The Google crawlers would index the respective page, as it contains the keywords, and the article would be accessed only by a limited number of visitors. This is a common practice, so don't be surprised if you find a solid website with great articles, but also with a bad section that contains only articles giving you headaches.
Another method to use those articles is to correct them. I am the kind of writer that doesn't like to get back on his work, but there are some webmasters that just can't do it other way. Those webmasters buy bad articles with low prices, giving them to a native proofreader for modifications. On the other hand, it is not such a great deal. A bad article with a cost of $1 might need solid corrections, and a native corrector would request at least $2 to modify the respective article. Total costs would be $3 for an article. With this kind of money, you can find writers (like me), who are not perfect in English, but whom can write good articles for any kind of internet site.
As a conclusion, it is a good idea for a writer to learn how to write SEO articles better, instead of dealing with bad content. Moreover, Google introduced some new algorithms that are able to detect bad content; therefore, it is better to have a website with quality content all over, instead of having a section with bad articles.
A writer that is able to write SEO articles with limited English notions can always improve his or hers skills. Let's see some methods that would allow you to write good content articles after a while.
Always listen to your clients
If you are a beginner and you have just wrote your first SEO article, your client might have better notions of English than you, therefore he or she might send the article back for proofreading. Correct the article and keep the advices of the respective person in mind. You would never guess how many important and interesting facts you might find out about writing just by correcting your own articles, considering the specifications of clients.
Find guides and English courses online
It is not that hard to learn how to write SEO articles. You just need a few notions about keywords, density and page arrangement. The level of English is much more important. Don't stop writing, but whenever you have some free time, use it wisely and study the free English guides available on the internet. You might even want to find the paid guides, which are more effective, but make sure to spend your money wisely.
Read a lot. English articles, news and guides are perfect to improve your English level. However, there is nothing better than a solid guide is.
Watch movies in your own language without subtitles. This way, your brain would "train" itself to translate the movie. This empiric method was used by many writers, and it is the perfect method to improve your English at conversational level.
With all those aspects in your mind, you will be able to write SEO articles effectively after a while, and to improve your content article writing style, allowing you to write for more money.