1. Set a goal
Setting a goal is very important while learning a new language. What do you actually want to learn? Do you just want to say 'hi' and order a meal in a Japanese restaurant or do you want to understand your favorite Japanese movie? If you go for the first one, you only have to learn some grammar and the vocabulary of words you are using in the restaurant. For the second one, you have to dig deeper into grammar and learn more vocabulary.
Learning a language can be simply compared to losing weight. If you don't eat healthy and ignore your workout schedule nothing will change. This is somehow the same as learning a language; if you don't study and don't practice you will learn nothing. Start with infusing your new language into your daily life. Spend 30 minutes per day for studying and have a rest day on Sunday. Listen to music in your new language and look at the lyrics. Watch movies and listen concentrated while reading the subtitles. Make grocery lists and count numbers all in your new language. Think about when you want to reach your goal and make a schedule. Be pro-active and stay consistent.
This is one of the hardest things to do. Maintaining the new language. If you don't know someone who speaks the language you learn, find a language buddy online so you can practice. The best thing to do is write everything you learn down. You will buy a lot of books, find a lot of online information and hear a lot of new things. It is obvious that you can't remember everything straight away so write everything down in your own ' language book'. Go trough the book every week and try to remember everything little by little. And if you are ready for it, combine tip #1 and #2 to set a new goal so you can challenge yourself.
I hope this will help you!