Can you hear the difference in Chinese? I've noticed that students who have difficulty distinguishing these sounds in Mandarin also have trouble in English. Do you hear the difference when a Chinese speaker says 您nín vs. 林 lín? Speaking, many Chinese people have trouble making the "l" sound strong enough at the end of words (I suspect this is because Chinese words don't end in this sound). So you need to make sure to stick your tongue far forward against your top front teeth to properly say a word like "will." Even better is to exaggerate and stick it out when saying this. Practice looking in a mirror and imitating a native speaker. These BBC videos are really helpful: http://www.bbc.co.uk/worldservice/learningenglish/grammar/pron/sounds/

All english words ending in the group " ine" can usually be pronounced as like the word "iron" Or even the word "eye" with the "n" sound on the end. It's rarely pronounced any other way, except on a few occasions when it appears in words such as magazine. The general rule is that it will be pronounced with the long I sound as in eye. If a double "n" appears in the word, than the "i" sound will be short, as in the word "tin" Also you will notice that if there is no "e" on the end the "i" is pronounced short as in "tin"

Well, the sound from "n" goes completely through the nose. The sound from "l" goes completely through the mouth. They really do sound different.