It's better to study both languages at college or uni.

The best way to learn a language is to live in the culture where that language is spoken. This method is called immersion. If immersion is not possible, then one on one tutoring along with other activities to simulate immersion is recommended. Fill your life with cultural experiences using the target language for a period of time. Getting together with other speakers in social settings, watching TV and movies in the foreign language or with subtitles, reading comic books and children's books and then more advanced readings as your skills improve, listening to songs and learning the lyrics so that you can sing along...all these things will help you build language skills. There are also chat rooms online like Paltalk. Find out who in your area speaks the language you want to learn and invite that person out for a treat and a chat or offer to babysit if they have young children who are already talking. I hope these ideas are of help.

in order to learn a new language, it is ideal to live and work among people who speak the language. However that is not always possible. When I learned Chinese, I would study from a book, and then try to use the things I learned with a native speaker. That helped me remember the things I studied and allowed them to correct any mistakes I made.