you have same trouble with me :(

and my tips just enjoyed it...

like watching english movie without subtitle,

chatting with someone in english..

listening english song is fun too.. etc.

just enjoyed it and be patient.

maybe thats can be so difficult, but thats fun..

Goodluck :D

Find a language partner and try to talk in English as much as you can.

Read in English.

Watch movies in English.

Learn EVERYDAY ( I mean do grammar and vocab excercises).

If you have a chance,go to the country in which English is a main language and talk witch natives.

Try writing short stories or small letters in English.  Developing vocabulary is always great, try learning new words; even native speakers try to do this.

Practice English by looking for contents and materials that are relevant to you, that you think gonna help you acheive your personal goals, that way you will find yourself progressing very well, and since you are a Math student why don't you watch math lectures from time to time, since you study math I think you like it so it's a good things to do which I did, I am a math and computer science myself and I applied that method it works very well.

1. Watch English films and TV shows, listen to English music

2. Practice reading, speaking to yourself.

3. Find a tutor who can correct your mistakes and clarify basic concepts for you.