Oh~ this is question is really hard to answer , I took a over view on this http://www.zhongwen.com/x/guopu.htm, it is so complexe. Some characters have different tones, but In most of case we using light tone is enough,In I think everyone would be understand what you mean.e.g 聽 we always say "ㄊ一ㄥ" ,nobody say "ㄊ一ㄥˋ". different tones cases is easy. the most complex case is one characters with different pronunciation, In different case and meaning must using different pronunciation, and In real cases you will see that very often in Chinese ,espicially in Simple Chinese. So in one characters with different pronunciation,I can not give you a good answer, becuase it do not have the right answer, it depend on which character with it's own answer. If you want to learn them ,you must have more oral practice.

A character can have multiple pronunciations due to historical or dialectal factors. Most of them are predictable depending of the word category or word context; however, there are some variance that just have to be memorized. 多 can be pronounced either in the first tone or the second tone (interchangeable) when it functions as an adverb: 多久、多美. Otherwise, only the first tone is used: 很多、多數. 刻 can be either the first or fourth tone when used as a verb: 雕刻、刻印. But only the fourth tone when used as a noun/adjective: 時刻、深刻. 聽 usually is used in the first tone; the second tone variance occurs probably only in Mahjong game: 聽牌. 玩 is used in the fourth tone only in 古玩, which is not a really frequent word. There are dictionaries an online resources for these kinds of variance. Try to search 破音字 or 一音多字, you might find some useful information.