Identify specific parts of grammar you need help with. You can do this by learning what kinds of mistakes in grammar speakers of your native language often make. For instance, some Spanish speakers will place the adjective after the noun when they describe an object, such as a "book blue" instead of a "blue book." Another way to identify where you can improve your grammar is to write a few paragraphs and ask a native English speaker to help you identify your mistakes.
Use an English grammar book or online grammar quizzes to help you learn how to correct the mistakes that you regularly make. Stick to learning one grammar point at a time. Master that point before you move on to another. When you speak in English throughout your day, remember the grammar point you are currently working on, and do your best to use sentences that properly use that grammar point.
Read as many different types of English language materials as you can. For example by reading novels, business articles, and recipes, you are seeing the different ways grammar is used in various types of writing. Take notes of the way that grammar is utilized in these materials, and begin to use the same types of sentence structures in your own writing and dialogues.
Join an online language group such as My Language Exchange to converse on a regular basis with native English speakers who want to learn your native language. Ask them to correct your grammar as you talk, whether it be in a live chat or by e-mail.