Having taught close to a thousand students of English over the past 20 years, my advice to you is to speak as much as you can in class, without caring about who is judging your grammar. You need to find out what your errors are and how to correct them, and the only way to do that is to speak the language for others to hear you and be able to provide you with corrections. Errors are good; recognizing them is the first step in learning how to improve your ability.
My best students, those who succeeded in becoming native like speakers of English, had the worst, and I mean the worst grammar--at times I could barely even understand what it was they were trying to expresses. I didn't care about that, however, because I know that making errors is a stage of learning. Teachers expect it. They need to know their students' weak points; otherwise, they can't help them improve.
If you want to know "how to" do something and be able to do it well, you have to practice. The more mistakes you make, the more likley you will be corrected and given the correct forms. If you're not making mistakes, you're not learning. It's as simple as that.
You need to speak English no matter how embarrassed you may feel about what you sound like or what people think about you when you speak. Feel comfort in the knowledge that millions of people before you have been where you are now and they succeeded in over coming their fears. You, too, can do it. Now is a good time to start!