Well, it depends. You might come quite far by following general advice like that you will get as an answer to this question but it would possibly be a solid waste of time as learning (a language) efficiently and successfully depends on many conditions like age, prior education, biological learning speed, social environment, motivation, material, teacher, fellow-students and health (possibly not complete). So the best advice I have after 12 years of teaching and having had to study more than 10 languages would be the same I give to people asking for a cure to their serious health problem: go see a professional (tutor). Look for the best. They are worth every single cent and what's more important, minute. It is a pleasure to work with pros.