When you first registered or logged in, you will have seen a choice of servers. One is "China", and another is "US/Europe/Asia". It should have automatically picked the closest one, but it doesn't always work right. Only use the "China" one if you're in Mainland China. If you're anywhere else, use the "US/Europe/Asia" server. Choosing the 'wrong' server may affect how fast things load for you.
If you're not sure which server you chose, then go to Settings > About > Connected Server, and make sure you've made the correct server choice.