. I learned by living in the other countries. Semi-immersion in your home country is possible (movies, books, tutor, conversation exchange) but harder.
. What's your goal? Business, pleasure? Focus on finding the vocab you need to know and figuring out what level you'll need to reach.
. Fluency in itself isn't a true state - ability to communicate clearly is the best gauge, most of the time this means spoken communication. This can range from simple formalities to industry-specific negotiations.
. Traditional reading and writing exercises are only useful to learn the language framework, i.e. its basic grammar. Try to get these out of the way quickly, and use them more as a reference.
. Modern novel reading is good for vocab and cementing grammar knowledge, as well as being amusing.
. IMO the key to the most important communication channel is learning to speak in a way that is received loud and clear by a native. This means learning the sounds of the language, phonetics, and seeing where they differ to your own sound-bank. A recent blog experiment I read about [http://www.xamuel.com/french-in-30-days-day-30/] made some interesting discoveries - his intensive daily learning only resulted in an understanding of many single words. His actual communication skills weren't functional. I'd say that they could have been, had he focused on the right things. I left my further thoughts on the linked page.
. You can do all you need to for effective learning every day, just by living in the foreign country, with no need for reminders - but this is of course rarely practical.
. A further key point: learn to hear the fixed expressions that are used in common speech. With enough of these you can sail through most situations and even learn to ask for help when stuck on something.
. Do not try to word-for-word translate what you want to say in the target language, find the fixed expression for what you want to say. This takes time, and a fair bit of practice, but what doesn't?
. Flashcards give the false impression of learning to communicate. I would avoid these unless they contained fixed, common expressions. Even if they offer spaced repetition, which seems to work well, they encourage the wrong kind of learning. Yes, adults can take shortcuts to learn faster than children/babies, but they still must learn the 'codes' of communication in the culture and language.
I'm working on a system that incorporates these points in an audio format, but it's yet to be tested and I've no idea if even that could work as intended. So far, no silver bullet.