How can I learn English better?

I've been learning English for a while. But it seems to me that my English skills and level don't improve.

I am self-teaching to get a TOEIC certificate, and the last time I tested, I got the same result as 3 times before. :(

The way I teach myself is by working on test books, I do 1-2 mock tests a day. I want to improve my Listening skills. I find it hard to concentrate, and I can't understand every word in the audio. Sometimes I can't even understand the questions and the answers in the Listening section.

Is there any way that I can improve these skills? I really need to have my TOEIC certificate by the end of this year. :( Please help me, thanks everyone!