Many non-native English speakers make a mistake choosing between get or become.
The difference is especially problematic for Japanese people, since both words can be translated as なる.
The difference may seem a little complicated at first because both words are used in the sense of "begin to be," however there is a simple rule.
Get is used with an adjective for a progressive state, this is when things are changing. Get is more common in recent spoken English. It is often used with a comparative (words with ____er, or more ___). Get does have some other meanings, but today we'll just focus on this one.
- The weather's getting colder.
- I want to get better at speaking in English.
- The stock prices are getting even higher.
Become is often used with a noun, referring to a complete change. The difference seems to be very large.
- The student became the teacher.
- New York has become a safer city in the last twenty years.
- The audience became so silent, you could hear a pin drop.
Both get and become can be used with adjectives, (he got angry; he became angry), but again, got seems more progressive and became seems more complete. Where do you draw the line? That's up to you.
One clear difference that is that get is far more common in spoken English. So if you are working on using a more typical spoken style, using get is a safe choice.
Just keep listening to how native speakers use get and become, and try to speak like they speak. It might seem tough now, but it gets easier with practice.