Don't, lego has gotten way too fucking expensive for what you get in the box. Go find something else to collect.
For example, I used to have a lego city on my desk, but over 400$ worth barely covered half of it. Then I saw these new match box city sets, and decided to collect those instead.
For less than 100$, I have completely covered my desk in a nicely detailed, dense little city.
Lego is dead, its become nothing but licensed shit. They don't do anything original any more, the only thing original left is ninjago, city, creator, and classic, and even those sucks harder than a blowjob from a black hole these days.