What really happens is that when you're growing up you learn your native language suggestively in your environment. In fact, learning a second language is harder than learning the third, fourth and so on. It happens because is just when you start learning a second language that you realize how few you know about the structures of your native language. Said that, is not the level of difficulty of the language or the number of languages that defines the learning process but the understanding of the structures. Once you know what you want you're be unstoppable.

I can't give any tips but have heard from others that once you've learned another language, your brain is 'trained' to learn languages, so learning more languages becomes easier. Your brain adapts. You pick up words and grammer quicker. I hope this helps.