This can be quite confusing for a non-native speaker to grasp, believe me, I am one. As it turns out, from what I've learned in my years of practicing the language, putting the adjective before the verb adds an endearing/abstract modification to the word.
How abstract, you say? Let's take a look at some examples:
Ella vive en la casa blanca
This is very straightforward, "the white house", the house that is white in color. So let's switch it around a bit and see what happens
Ella vive en la blanca casa.
In this case, there is a lot of emphasis on the adjective and the word "white" is open to interpretation now. In this case, we can begin to extrapolate and use the different meanings of "white" to describe this house.
Typically, when the word "white" is thrown around, we think of the color immediately (or the absence thereof). Sometimes though, the word is associated with "white" things like: angels, goodness, predominance, blankness, the list could go on in the same way we use the word "blue" to mean sad.
Consider there is a neighborhood of houses and all of them are exclusively made from bricks. Then, one day, a very rich and determined person decides to build his/her white marble house directly in the middle of this neighborhood. Now, to the immediate viewer of the neighborhood, this would just be "la casa blanca" since there isn't any kind of story attached and you are simply looking at the house at face value; it is white.
Meanwhile, the neighborhood looks at this house as if it were alien to them.
Everyone else has a home made of bricks while that white house over there sticks out like a sore thumb.
It may be a complete disgrace to the neighborhood, or it may be the most respected homes of the neighborhood. Regardless, putting the "blanca" in front of "casa" helps communicate this phenomenon.
Think of the difference between The White House, the presidential household, and the white house next to the green house.
El pobre niño quiere un peluche
That sentence is made to make you feel sorrow and pity for the boy. His financial situations are not a part of the sentence.
¡Ayudamos a este pobre perrito!
Let's feel sorry for the dog now. What a pitiful dog it is; you can see it's bones and it only has one tooth. This is such a poor quality puppy. Could things get any worse for this poor puppy?
Now, if we switch things around again and move "pobre" to the end, things get literal.
¡Ayudamos a este perrito pobre!
The puppy is poor, and by poor we mean "doesn't have any money". Let's give him some money. Let's help this puppy pay off his debts!
You can find an article concerning this phenomenon as well as more examples at the address below.