This (often at start of sentence)

Using this as a pronoun, especially when it is the  first word in your sentence, is often problematic. Consider for a moment the two uses of  the word.

As a pronoun, specifically a "demonstrative pronoun", it does what pronouns do, which is to replace a previously mentioned noun (known as the antecedent). In this respect, this is no different from the  personal pronouns he, she, I, you etc.

As an adjective, specifically a "demonstrative adjective", it does what adjectives do, which is to tell you more about  the noun that follows. In this respect it is little different from simple adjectives such as big, small, red, green (this apple,  red apple, green apple, big apple, this fact, important fact).

The problem arises when you use it as a pronoun, often (though not always)  at the beginning of your sentence. Whereas "He" at the top of a sentence is unlikely to cause confusion (a man will have been mentioned earlier), "this" often appears as a pronoun standing for "what I just said" or "the thing I just mentioned" or "the point/observation I just made."

The problem with this use is that the reader must now read back to double-check exactly what the point or thing just mentioned  was, and a reader reading backwards is a sign that your prose is not working.

So if you use "this" make sure it is followed by the thing it refers to:  "this issue", "this question" and so on.  Do so (this?) even at the risk of repetition of a word. If you cannot  find exactly the word you want because you are unsure what "this" really  refers to, then imagine how hard it is for your reader.

Quick rule: "This" at the start of the sentence - or anywhere else in the sentence, though the issue is most frequently encountered at the start - should always be used adjectivally (i.e. followed by the word to which it refers).

Once you start inserting the missing word, now  consider whether "this" is necessary at all. Might not a simple "the" do instead?

Here's an example:
Chinese capitalism turns out not to be in the slightest bit concerned with liberal values. This shows up the arrogance and  presumption of the experts who predicted that market forces would  bring democracy to China. 

Improved version:
Chinese capitalism turns out not to be in the slightest bit concerned with liberal values. This indifference to liberal values shows up the arrogance and  presumption of the experts who predicted that market forces would  bring democracy to China. 

Alternatively: 
Chinese capitalism turns out not to be in the slightest bit concerned with liberal values. The Chinese indifference to liberal values shows up the arrogance and  presumption of the experts who predicted that market forces would  bring democracy to China. 

Here is an example of the "this" appearing later in the sentence, but posing the same problem:
The key point Diaz is making here is that this is problematic because physicians, like everyone else,  are misled by marketers.

 

The solution, as  before, is to define the "this" - to use it as a demonstrative adjective rather than as a pronoun.

The key point Diaz is making here is that this aggressive marketing of off-label pharmaceuticals is problematic because physicians, like everyone else,  are misled by marketers.