While I like to do things online, as far as learning Chinese is concerned, the most effective way of learning the language is still immersion.
To immerse yourself in Mandarin, put yourself in an environment where Chinese is the primary tool for communication.
In this way, you get to hear how the language is spoken, and respond to it in a spontaneous way. It is ‘live pinyin online’. There are ample opportunities for you to make mistakes and grow. Practice makes perfect. When you are forced into the situation where you’d have no choice but to open your mouth and speak Mandarin most of the time, the learning process becomes proactive. This is extremely powerful. Some of the best cities to immerse in Mandarin are Beijing and Shanghai. Other cities to consider are Taipei and Singapore. It will be more effective if you can sign up a language course when you are there.