That's a good question. The only way I know one can learn to ride a bike is trying to ride a bike and eventually one day you're going to be able to ride a bike with proficiency, of course, during the process you're going to fall and make a lot of mistakes, which is normal, that's ok because you're gaining experience, so the only way to improve your speaking is precisely speaking. I've actually been in the same situation as you, I was petrified and speechless during a conversation with native speakers because sometimes I got the main idea of how to express some feeling or idea, but I didn't remember one or two crucial words to express the idea that I just had in mind, or even I knew the word, but my pronunciation was so bad that the other person in front of me didn't understand what I want to say. Now I've realized that you don't have to lose your cool in these situations, the only thing you have to do is just explain your idea with other words, it might mean that you sound weird or unnatural, but the important is that you've conveyed your idea to the other person, and then this person can suggest another way to say it. I remember one time, a Canadian and I were talking about our plans for the next day and I uttered "Tomorrow I going to make my laundry" and the other person said "Oh, Did you mean to do your laundry, because to make your laundry means that you're going to make sure you dirty your clothes", then we booth laughed about the misconception, it was funny. I would recommend you don't be afraid of making mistakes, if you made one, then just smile and try again, thank the person front of you if he/she gives some feedback and learn from your mistakes. Long story short, the more mistakes you make, the more experience you're gaining.