Q:

The two pronunciations of 粘

粘 can be read as either "nian" or "zhan", but in both way it can be translated as "sticky", so what is the difference?
In other words what should I take in mind, when reading a text , in order to understand which pronunciation I should use?

A:

Originally, you had two separate characters (zdic links):

粘 = zhan1 = (v.) to stick
黏 = nian2 = (adj.) sticky

The usage distinction still remains, but it is now acceptable to use 粘 for either word. Unihan lists the characters as semantic variants.

A:

I was taught at class, that zhan is the reading when 粘 is used as a verb, 'to stick, to glue'; the more common reading nian covers almost all the other cases, when its used as an adjective, 'sticky'. But I think this is not entirely correct. 
Here's a long list with compound words. In most cases the reading is nian, in some cases zhan. Try to see if you can find a rule. 
Interestingly, the Taiwanese Education Ministry's dictionary only lists nian as reading. 

