If you are a beginner, it is very easy to achieve to intermediate level in a short term, maybe it just needs 3 months. When I was a beginner two years ago. I read grammar books. and practice writing almost everyday, and practice pronunciation, even when I drove. My recommended as below:
1 . Pronounce each new word correctly, and try to read articles everyday, not less than 30 minutes.
2. Practice writing, and ask a native to correct your articles.
3. Read grammar books in details.
4. If you feel confident about the above three terms, then try to strength your listening skills.
All above suggestions just used for beginner, if your English ability is above beginners, then ignore all my suggestions.