Choose your time zone. Every night at midnight in your time-zone, we take a snapshot of your progress so you can measure your progress over time. (We guess your time-zone when you sign up, but it doesn't hurt to double check). You can set your time zone in your Profile.
Assume Knowledge. By telling us what you already know (from your pre-Hack Chinese studies), we can help you be even more efficient with your time. The questionnaire you filled out when you joined should have done this for you, but if you think the vocabulary we assume you know needs some adjustments, read this article on Assuming Knowledge.
Familiarize yourself with "Spaced Repetition". Many people are specifically searching for an SRS tool when they find Hack Chinese. If this is you, you're probably all set.
If you aren't quite sure what SRS is (and why it's so powerful), check out this simulation: