I don't ever learn two languages at the same time. I've been learning Polish now for many months and my teachers are very impressed by my ability to understand cases, spelling, and general grammar very well. I don't want to give up learning Polish and I study on my own too.
However, my grandmother doesn't have anyone to talk to her in other languages. She loves languages and was happy just to hear me say a few words in Polish. She seems proud of me for caring about learning the languages of our culture, but she cannot speak Polish. She speaks English, Russian, Ukrainian, German and understands Polish. Since Russian and Ukrainian are so similar to Polish and would cause confusion at this stage in my learning, I decided on German. It helps that I already know a bit of German, so I'm getting through the first book I acquired pretty quickly since it's mostly review.
I really do want to learn German, and this gives me a good reason to be serious about it. But I hate the idea of focusing on german and Polish at the same time and possibly not progressing as much in Polish.
Also, it will be hard for me to feel like I'm making progress in Polish if my ability in German surpasses my ability in Polish (which it most likely will since German is much easier and is extremely easy for me to pick up), since it'll make me feel like I could've been devoting that time to Polish.
Does anyone have any ideas on how to study both but make Polish my main language to study? Any experience with doing this before?
once upon time I studied English and Russian - English was my focus and Russian was obligatory - I was sort of gifted language wise and Russian is similar to Polish (although most vocabulary has to be learned, you still have very similar grammar to deal with) - I learned some Russian without much effort - my English is much better though cause I spent a lot time learning (in school), reading and using it (especially after the advent of internet). - I don't know if that helps you - but if you acquire German quite effortlessly you can then focus on Polish (for whatever reason you choose to)
Merely a gentle word of caution. Learning TWO Slavic languages simultaneously could be a recipe for disaster. False friends between, say, Russian and Polish, abound and often the basic word stock is different enough to cause extreme confusion. Even the grammar between related languages is not always a safe bet for mutual intelligibility.