I believe I have the same problem as you. Sometimes I even think that I will never learn grammar properly, especially the advanced one. I make too many mistakes despite having been learning for a few years, in my opinion at least, but people tell me I tend to exaggerate.
Of course, I know it would be fantastic to have a conversation with someone who wouldn't be angry at me and my mistakes, but it's difficult to find such a person. It would be also beneficial because of the fact that during such a conversation (and I'm simply talking about writing, not necessarily speaking via Skype or other means) people are forced to frequently use many words they wouldn't othewise, therefore they are no longer known passively.
Actually, I have a question. Is is a good idea to translate some texts into native language and then back from Polish, in my case, into English, and then compare the translated text with the original?