English language is not very easy to master. Studying grammar might slow you down and confuse you. You will think about the rules when creating sentences instead of naturally saying a sentence like a native. Remember that only a small fraction of English speakers know more than 20% of all the grammar rules. Many ESL students know more grammar than native speakers. I can confidently say this with experience. I am a native English speaker, majored in English Literature, and have been teaching English for more than 10 years. However, many of my students know more details about English grammar than I do. I can easily look up the definition and apply it, but I don't know it off the top of my head.
Many scholars learn vocabulary and try to put many words together to create a proper sentence. It amazes me how many words some of my students know, but they cannot create a proper sentence. The reason is because they didn't study phrases. When children learn a language, they learn both words and phrases together. Likewise, you need to study and learn phrases.
When learning a language the most important aspects to master are: Reading, listening, and speaking. The same is true for English. However, speaking is the only requirement to be fluent. It is normal for babies and children to learn speaking first, become fluent, then start reading, then writing. So the natural order is listening, speaking, reading, then writing.
Being able to speak a language is not related to how smart you are. Anyone can learn how to speak any language. This is a proven fact by everyone in the world. Everyone can speak at least one language. Whether you are intelligent, or lacking some brain power, you are able to speak one language.
A common phrase that is incorrect is, "Practice makes perfect." This is far from the truth. Practice only makes what you are practicing permanent. If you practice the incorrect sentence, you will have perfected saying the sentence incorrectly. Therefore, it is important that your study material is perfect and that is commonly used by most people.