Online English Lessons are definitely effective. Reading books and studying on your own surely helps, but practicing your English skills with someone who is skilled enough in English would be better. First, you need to find the right teacher. You might find it difficult, but, hopefully, soon enough you can find one. Next, clarify to the teacher what you want to learn in class. Set your expectations. Lastly, practice using the English language as much as you can. You can listen to English songs, read more English books, chat or have informal conversations with people who speaks the language fluently, listen to English audio, write sentences and let your teacher give feedback, etc.

The thing is you need constant practice using the language if you really want to be good at it. You can't just get into an online class, and expect to be a great speaker afterwards. Like you have said, you will need a lot of time for that to happen.

I hope that helps. :)