Having a path is the best way to go. First, set your goals. Why do you want to learn the language? Is it a short-term reason (“I need to pass at least N4 to be accepted at this job/school”, “I want to learn just the basics in case I plan to go to Japan”, etc.) or long-term (“I need at least N2 to have an edge in Japan”, “I am really passionate in learning the Japanese language and their culture”, “I want to be a Japanese. Lol”, etc.). If you’re aiming short-term, Wanikani, Duolingo, and Bunpro will suffice along with watching anime or dramas left and right, but if you want to go long-term then you have to supplement yourself with textbooks.
Going that way, you have to learn to read and write Hiragana and Katakana first for a about week, and then you can start with Genki as was suggested by our other community members, or Minna no Nihonggo I and II. Each volume has a Japanese Workbook and an English Guidebook. If you can’t afford having a personal tutor due to a busy schedule, you can self-study. For each lesson, read the Vocabulary section of the English book first, list them all on an app like Anki or Japanese so you can quiz them, proceed reading the Grammar guide, and then off to the Japanese workbook. Finishing a chapter might take a day or three and each volume is comprised of 25 lessons. After lesson 50, if you’re doing it with consistently with Wanikani for your Kanji comprehension, you can pass the N4 exam. The book has a CD for listening practice.
For N3, you have to pick a path again. I finished Tobira and its workbook and got a good vibe during the N3 exams last July. I started learning last June 2017.
Step 1: Learn Hiragana and Katakana
Step 2: Consistent Wanikani (and others if you wish so)
Step 3: 初級 (Beginner) textbook (Genki, Minna no Nihongo)
Step 4: Listening practices
Step 5: Improvise and always question.