When starting to study grammar, it is important to select a few basic principles to focus on first. Here are some of the foundational concepts to begin with:
Parts of Speech: These are the kinds of words used to make up sentences. Learning how to identify the nouns, verbs, adjectives, pronouns, adverbs, conjunctions and interjections will help you improve your grammar.
Sentence Structure: Once you understand the different parts of speech, being able to correctly structure those parts into proper sentences is essential. Study the different types of sentences: declarative, interrogative, imperative and exclamatory.
Punctuation: Punctuation is one of grammar’s major components and its importance should never be ignored. Proper usage of commas, colons, semicolons and periods will have a huge impact on how accurate and readable your writing is.
Grammar Rules: To understand grammar accurately, it is important to learn the rules that govern its use. Each language has its own rules, so take some time to read up on those that apply to your native language or the language you are studying.
Studying grammar can be daunting, but it doesn't have to be! By studying these four topics first you will be able to get the basics down, and then progress to more complex sentences and grammar principles.
For more information, I recommend this guide by Grammarly: https://www.grammarly.com/blog/how-to-improve-your-grammar/