Here's the scenario. If I write an article and submit it, for example let's say to an articles directory site like articlesbase.com, and then post that exact same article on my blog. Will google consider that article as duplicate content on my blog? Will it drop my rankings? Thanks!
You will have less chance of getting a hit on that particular blog article as the SEs will probably choose one of the other copies. Overall, if your blog is mostly original it shouldn't hurt you at all.
Ideally you should post the article on your blog first before submitting it to other websites or article directories. I doubt it will affect the rankings of your main blog page, but the page for that particular post may not rank as well in that scenario. Duplicate content is more of a problem when most of your content is already indexed on other websites. One blog post shouldn't matter. Search engines understand that there are circumstances when some content needs to be repeated.
And don't post the whole article in article directories, use the introduction in article directories then link to your site for the whole article.
As many pros recommend, it is the best practice, to post an unfinished article in sites like articlebase and then place a link to your full article in your blog/website. In that way Google would not consider it as duplicate content and you would be getting more traffic from the Read More link in your article. Regards.