A native speaker uses all this stuff regularly when they speak. The most important thing is that you're actually using it. You should use used to a lot, so that it isn't confused with another word. Used to also doesn't have a d in negative or in question forms. So i didn't smoke any more, because it's very bad for your health. I used to smoke, but then i gave up. This is something really useful. Now let me tell you about to be used to doing something, or i am used to do something, right? Which is totally different from just used to and not used to. For example, i'm used to living in london -