Personally, I don't insist on rule-book correctness. But, I have a general philosophy:
'KNOW THE RULES BEFORE YOU CHOOSE TO BREAK THEM.'
So, often, intentionally using wrong constructs increases the beauty and expressivity of your sentence by adding an element of humour. But that should be done sparingly and wisely. It should, in some way, make it clear that you are aware of the rules you are breaking.
Thoughts in the mind are abstract entities. Communication is the amazing process of the tranformation of those abstract entities into concrete ones: through words and sentences, through facial expressions and actions, and through various forms of art and science. Don't think of mastering a language. Just try to observe and marvel at beauty of man's effort to try to map the abstract internal world with the concrete outside world.
And finally, communication is more or less independent of the language. If you are good in one language, you will be good in all. If the mind is eager to always communicate an idea with precision and beauty, language just falls into place. Think about being a good communicator. Read the books and papers you have always been reading with a different perspective: With the perspective of understanding the way the authors try to convey their thoughts. You will soon be a master communicator yourself!