The internet is littered with websites claiming to teach you the language within ridiculously short periods of time. However I’ve generally found there aren’t many shortcuts to be had. I found it extremely useful to first learn the basic grammar points. Although this may not sound like much fun, it doesn’t take too long, and it enables you to have a very solid template to which apply the language, and in the long term will actually save you time. For example, I studied the German language, when it comes to verbs there are perhaps 4 or 5 variations of the infinitive form, depending on the subject (I, You informal and formal, We). However the changes that are applied to the end of the verb are consistent with each and every verb, (par a few strong verb exceptions). Once you’ve learned these changes then additional learning only requires you to memorise one word, which you can then adapt yourself.
I also think its important to practice what you have learnt, although this is not always that easy if your not residing in a the same country as the language you are learning, there are a few other ways. There is the possibility of creating a pen pal relationship, through the internet. There are thousands of people around the world wishing to learn English, so finding someone in the country of your chosen foreign language shouldn’t be too hard.
For those of you not residing in your chosen language country a good method for increasing your knowledge of the language and keeping your skills active are by learning and practicing a new word each day. Simply reminding yourself a few times a day and practising in pretend situations should help keep your skills intone for when you get to next visit the country!