Many people wonder what is the fastest way to learn to function effectively in a foreign language.
Intensive language study, either in a foreign country or in a special course which meets for six to eight hours a day (and would ideally involve evenings), is clearly the fastest.
There are many reputable schools in Europe, Africa, Asia and South America which offer intensive language classes to foreigners and these are an effective, but exhausting way of learning a language quickly and well. The best of them combine work on accent, grammar, phrases, speaking and writing, and insist on your only using the target language even outside of class time. Some will send you out into the community for a number of hours each day with the goal of getting speaking practice, some offer opportunities to stay with local families so that you are speaking and hearing the language throughout the day. This strategy is probably the fastest way to learn.
A similar, less formal, alternative is to find a language teacher and conversation partner, and set up your own intensive language course. This can work well in places like South America, Africa and Asia where it enables you to live outside the capital city where most formal courses are located, and where labour is relatively cheap. But it does require either a contact who will set things up for you, or a lot of trial and error. It probably works best if you have put some thought into the materials you will need beforehand as you will need to guide your teacher, but if you are disciplined you can make amazing progress in this way as long as you have a teacher who will correct your accent and faults. The advantage of this is that you can study in a rural area where living is cheaper and people have more time.
This is not quite the same as pure immersion learning, where the learner is paired with a language partner who speaks no English and left to work out how to understand what is being said to him, and how to respond. Immersion language learning probably works if the learner can persevere long enough, but is just as likely to result in massive frustration and misunderstanding. It is not really a fast method of learning to speak a language well.
If you cannot afford the time or money to do this immediately, or if you have a few months before you leave, it is worth investing in a good language learning course, a basic grammar and starting your study immediately. That way when you arrive at your destination you have some grounding and are not starting at zero. Even those hours in high school studying Spanish or French where you think you learned nothing will not be wasted because they will give you some foundations on which to build.
Intensive language study courses are mentally and emotionally exhausting, but they are the fastest way to learn a foreign language I know of. Pairing them with some pre-study will make your task much easier at the start, and will help you to progress faster. If you are going into a course with several other students, it will also help you to place into a higher class and reap greater benefits in a shorter time.