Meet with your English teacher. Tell him what specific English grammar concepts you're struggling with and ask how you can improve. While the teacher is giving you pointers, take notes and ask questions if you're still unclear about what was said. Also ask for some study guides and practice worksheets to take home.
Purchase an English dictionary and phrasebook. Purchase a dictionary and phrasebook that has both your native language and the English translation of the words and phrases in that language to make learning English easier for you. To make it fun, get a voice recorder and create a short audiotape of yourself using the English words and phrases you learned.
Read English-language magazines and newspapers. Pay special attention to how sentences are written in English, as well as how common nouns, proper nouns, adverbs and adjectives are written in the articles you read.
Practice writing in English. For example, if you want to become better at conjugating English verbs, get your English dictionary and write a list of the verbs you are struggling with, study the conjugations of the verbs and then create sentences with these verbs.