Addressing people properly in the work place
Addressing your work colleagues
In state-owned or private enterprises, it is common to use people's titles to address them, e.g., 王行长 (Bank-Governor Wang), 李总 (Chief Li), 陈经理 (Manager Chen), 张组长 (Team leader Zhang).
To address your peer colleagues, you can also use 老李 (Senior Li), 王大姐 (Big sister Wang), 史老师 (Mentor Shi), 陈师傅 (Master Chen) for those who're older than you, and 小李 (Junior Li) or their full name for those younger. 老师 (teacher, mentor) is an especially common term used in banks, accounting companies and finance departments in enterprises. The addressee does not have to be a mentor, and experienced staff usually use this term to show respect for expertise.
In foreign enterprises people tend to call each other by their English names, regardless of age or rank. You'll meet Cherry, Jasmine, Echo, Leaf, Bright, Macro, Spark, Phoenix… People choose their own English names (sometimes a simple translation of their Chinese first name). These are not their real names, but they are easier for foreign contacts to remember. They might even use their English names, instead of Chinese first names, on their business cards and on emails.
Addressing people on formal occasions
On formal occasions such as conferences or when meeting clients, you need to address people using 先生 (Mr), 女士 (Ms) and 小姐 (Miss) after their surnames.
先生 is age irrelevant, but 女士/小姐 can have different regional usage. In northern China female professionals like to be called 女士 while in southern China 小姐 is used far more frequently (even for married women in their 40s). This would be frowned upon in the northern provinces because of its 'street girl' connotation.
On the other hand, if you know that the person you are addressing is in a senior position (i.e. a general manager, a director, etc.) but do not know which position specifically, you can always address them as 总 (chief), also placed after the surname. Note that even if a person is in a deputy position, you still call them 总 instead of 副总 (副 means deputy, vice-).
When you know people better they will let you know what they prefer to be called. 叫我Andy吧！(You can just call me Andy!)