I'm currently living in Poland. I spend my free time (czas wolny) with Polish friends, buy my food (jedzenie) from Polish shops (sklepy), drink my beer (piwo) in Polish bars, exercise in Polish gyms (sala gimnastyczna), ride on Polish transport (transportu) so on and so forth ad infinitum. Part of the reason for this is that I am trying to achieve fluency in this often scarily daunting language, with all its fancy noun conjugations and verbal tweaks; slowly though, I think it is working.
The more I get stuck speechless in my local off licence, after greeting the assistant with a hearty dzień dobry (I don't drink enough to be using the informal cześć, I promise), and hearing a seemingly twisted and unexpected reply along the lines of 'można zamknąć drzwi proszę' ('can you close the door please', one you should remember in the depths of Polish winter weather), or zamykam sklep (I'm closing the shop now), the better I am getting, and while these situations are awkward - for a while - you will soon know when to swiftly lock the cold out and can get on with buying your beer. This is because it's true, that old-flung saying, that generally people learn faster when placed in testing situations, and what could be more testing than complete immersion in your target language's hunting ground?
There are multitudes of learning styles and teaching methods out there, each with their own purported strengths, and unmentioned weaknesses. Here, I will try and share some of the techniques that have worked for me, to show you how I have approached the various aspects of Polish language learning.
First off, while grammar is absolutely essential to any language, and some may argue particularly in Polish, with so many conjugations and rules (not to mention exceptions to the rules) to learn, this was never going to be a small task. It's true that the native Poles derive some humour from the misshapen syntax, erroneous verb endings and child-like case use adopted by non-native speakers and learners, but from experience I guarantee that this is all in good faith, and wholly light-hearted; anyway, how do you expect to know you're wrong unless your use of piwo instead of piwa isn't met with a light chuckle or satisfied grin from the barmaid? My advice: Embrace the Poles' willingness to criticise your learning, and be grateful they have a culture which will correct you when you’re wrong. There’re plenty of countries where this wouldn't happen and you could be proudly calling yourself a doughnut JFK style with, simply, no idea, ever.
It's been said that most native or fluent speakers of any language only ever use somewhere between 3000 and 5000 words, ever, in their life time. While this may not account for the most articulate of us, it does highlight how easy it can be to get your vocabulary up to standard. Granted, this won't magic your speaking and writing into grammatically infallible productions, but it will be the strongest arsenal you have in achieving fluency through practice; the more words you know, the more flexible you can by in your production skills (writing/speaking), and the more options you have in terms of syntax and grammar, when it comes to expressing your meaning.
If you memorized 10 words a day for the next year, that would bring you well within the estimated vocabulary usage of a native speaker, and trust me, with the right methods, 10 words a day is not overreaching - especially if you adopt the right learning approach. For example, look at the first paragraph of this article again; see how I repeat, perhaps unnecessarily, various words in Polish (czas wolny / piwo / sklepy etc.)? This is one of the most effective ways to remember: through repetition. I have a day-to-day spread sheet set up where I list the vocabulary I've learnt each day, in order to cover it up the next and see if I can remember the Polish translation - once I can do it without any help I consider the vocabulary conquered.
It's also useful to learn vocabulary in categories, definitely acquaint yourself with the rules surrounding noun gender in Polish (this will help no end when it comes to applying cases to your nouns), and – perhaps most importantly - always remember your motivation for learning, as this is the catalyst that first got you to pick up that book and begin; language learning is nothing without ambition!