The only way to learn new language is just speaking. Grammar is nice but for teachers who wanna improve they skills and unfortunately useless for beginners. Writing or grammar will come naturally with time.
Good idea is also start learning with writing down words which sounds or spell the same as Polish words or some funny meanings in Polish language.
The most important is practicing it as often as possible. At the beginning good idea is start watching well known films in original language. E.g. if you wanna learn British English watch Monty Python's Flying Circus and if you wanna learn American English watch Married with Children.
And last think, courses or schools aren't enough for learning language and it's always better to have some fun.