Well, I think the same rule(s) of thumb applies anywhere when it comes to applying for design jobs. The most important is to prepare an immaculate resume (please spell check this, and make sure the grammar and spelling are 100% correct. Layout / typography counts, so does content hierachy) and a solid portfolio.
As a junior, firms are interested in your potential to learn and grow with the firm, and don't get too bummed if firms don't hire you. It might not mean your work is not good at all.. just not their "style". Make sure your portfolio is organized and structured. While you don't have to shell out hundreds of dollars for a designer portfolio-binder, having a decent leaflet folder with good work, that's organized and labelled are important. You are in a market where work is related to packaging and appearance, so your work should be able to speak for itself with the best presentation possible even if you had a flu and cannot speak during an interview. Dress politely to an interview, business casual is fine.
While I cannot really tell you how the work environment as a junior is like in Hong Kong, my experiences as a junior in Toronto taught me a few things:
1) be humble - you have LOTS to learn
2) listen
3) OT's are not avoidable, so you might as well gnaw through it
4) if you screwed up, let someone know, don't try to fudge it
Good luck, the field is highly competitive and very cut throat! I am starting my first in Hong Kong as Sr. AD
