Studying grammar can be tricky. It’s different from vocab in that once you’ve memorized a word and know the meaning, you can use it and recognize it as needed. However, grammar can’t really be properly learned in isolation like individual words can be (though vocab is also more easily learned in context). Grammar is very much use it or lose it.
To start, if you have a textbook or workbook that you use to learn grammar initially, make sure you do all the exercises in the book to practice forming it. But once you’re done with the workbook, what then? Making flashcards with the grammatical form on one side and what it means and when it is used on the other side could be helpful. When you review a card, write down a few practice sentences—maybe three to give sentence—using that form. It would be even better practice if you can try to write a short paragraph using the form as much as you can.
If you don’t have a native speaker of the language nearby to help you check, Lang-8 can be a great site to have your work checked. This is especially important when you get into more advanced and less commonly used grammatical forms. By using the grammatical form and getting feedback on your usage of it, that structure gets reinforced in your mind and the process of using it becomes more and more automatic over time.
I hope this helps! Happy studying~