1. self-confidence: there is no better way to show your seniority than self-confidence: feel at ease in any situation. 1). don't avoid eye contact; 2). Smiling: I think all chinese women would do this. But sometimes it is a timid smile that makes people wonder if that is a smile or just the person doesn't know what to do. 3). speech: be assertive, avoid words showing uncertainty like probably etc. raising voice a notch could help here. 4). engage in conversations and show your knowledge base.
2. with all that, professional attire and other details. sometimes older appearance would help. being too shationable would give others impression of being young and by extension, less seniority. Asian people tend to look young. So need to pay a little attention here.