We were always told that we should not begin a sentence with a conjunction, and yet we are seeing it more and more these days. Is it okay or not?
There's one school of thought which belongs to prescriptivists and the other who adhere to the descriptivist camp. The former may be considered a bit old school while the latter where it's at. Descriptivists will tell you that it's perfectly okay to begin a sentence with a conjunction, just as long as it works.
However, this is the case when you're writing a novel, an article such as this or some other sort of non-formal and/or artistic type of thing. On the other hand, it's probably best to stick the prescriptivists when it comes to matter of academia, such as in an essay.