Well, you can either study and try to apply rules to everything, or you can start speaking with natives and learn through error correction. I recommend the latter, personally. It's a lot more painful and embarrassing early on, but it will allow you to develop a natural ear for the language and simultaneously get constant speaking practice with it. Studying books may allow you to write flawless complex sentences in one try, but you're not going to be able to speak it very easily at all, and you'll be constantly trying to apply complex grammar rules in your head instead of just learning and speaking like a native does. So find an English speaker (or several) here who wants to learn Indonesian, set up some Skype practice with them, and your grammar will improve quite quickly.

I agree with Grant: dive in and enjoy the language. :) However, you must pay attention. Take a look at your corrected sentence below. Lazy writing and speaking turns out... well, lazy. "How can I improve my English grammar easily?"