的-地-得, when do you use which?
The usage of “的” is in possessive or adjectival context.  E.g., (posessive) “我的狗”, or (adjectival) “真正的生意人”.  Generally a noun is modified, so a noun follows it, unless it doesn't, such as “有点儿不足是难免的”, (some insufficiency is unavoidable) which is still an adjectival modifier (unavoidable), even though it modifies the noun (insufficiency) in front of it.

“地” is used usually as an adverbial modifier, following the modifier and preceding the verb.  For example, in “她伤心地说” (she said sadly).

The last one, “得”, is distinct, because it's a potential complement, not a modifier.  It follows a verb to show the result.  So the structure is VERB + 得 + RESULT.  One of the things I found confusing about this, coming from English, is that it leads to some structures that have bit of repetition.  So to say "she speaks Chinese very well", you use something like "she speaks Chinese, speaks very well", i.e., “她说中文说得很好”.

Since both “得” and “地” come between a verb and something else, they can be easy to confuse.  But just remember that if "de" functions as an adverb, the verb comes after it and “地” is appropriate, but if you are trying to complement or completes the verb that precedes it, then use “得”, even in weird cases like “好得很”! 

For short, just remember: “地” usually appears before the verb while “得” appears after the verb. eg. “这件事漂亮地完成了。” and “这件事完成得漂亮。”  these two sentences are correct in grammar, although they have slight differences in emotion.