First of all don't contact just anyone. Contact only the people you find interesting and you can help too. Why do you find this person interesting? There is your conversation topic. Maybe it's not what the majority does and maybe there are other ways but at least for me discussions and notebooks may be the best way to meet people here. I'm much more likely to answer a message from someone I know from discussions, especially if they write interesting things, seem like a nice person and if we have had some interaction. Compare a complete stranger approaching you to chat, with someone you know approaching you to chat. It's like that. If you see someone wrote something in their notebook and you have something to say on the topic you can comment on it, and you can comment on discussions that you like. Gradually you will find people that you would like to know better and if you are interesting to them too starting a conversation shouldn't be too hard. Another good way to meet people and show that you are a nice and helpful person is helping with your native language by correcting notebooks and answering questions. You can also read profiles and if you find something truly interesting about the person you can comment on it. Another important thing is you should only try to contact people you can help with a language they are learning. So if someone is not learning Chinese and either not learning English or their English is much better then yours it probably doesn't make sense to contact the person. Arguably, it's even a bit rude. Keep in mind that like in real life finding the right person and making friends takes time. So whichever approach you choose, don't expect instant results.

Many people say "how are you" or "where are you from" actually does not interest me at all to talk with them in the coming hour instead I wish there will be more interesting stories that the correspondent is going to share with me. After routine acknowledge, I prefer to give the language partner a simple question to answer: Do you have concrete plan to carry out our English practice? Concrete plans mean time, schedule, ways or topics to be referred and so on. If the correspondent cant hardly say a word about their plans, more than likely the conversation cannot sustain long enough to interest me in contact with this person again.

It might be very cruel but after a series of contacts with many anonymous self-declared serious learners, you will see what I am relating to. 

@Luica you know what, there is no access to YouTube in China.

You can search on YouTube about how to keep a conversation with a native speaker, with someone who you don't know much about. You'll find a large list of videos and I'm sure, they'll help you a lot! There are pretty interesting and simple ideas. 

I would say: topic that matters. Think about the other person coming from another country who might carry totally different traits from yours, then you may see how important it is to find a workable topic for you both. If there is no topic that interests you both, your conversation is doomed to failure. That is often the case that many casual conversations can hardly go on for more than twice.