How to pronounce 'N' and 'L' correctly?

I have problem differentiating N and L. I pronounce them almost in the same way, except that there is nostril sound when pronouncing N. I think my method is wrong. So I look for some online teaching material. Here is what I found

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http://www.say-it-in-english.com/BasicEnglish7.html

To pronounce N:
put the tip of your tongue against the gums behind your top front teeth, raise the center of your tongue, vibrate your vocal cords, and release your tongue without a puff of air.

To pronounce L:
put the tip of your tongue against the ridge above your top front teeth, vibrate your vocal cords, then quickly release your tongue.
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Is the above method correct? So we need to raise the center of the tongue when pronouncing "N"? Can anyone enlighten me on this? Thanks in advance!

The tip of your tongue is at the same place for N and L and you don't release your tongue for either of these sounds. That's only the case with plosives (P, B, T, D, K, G).
The difference between N and L lies in the airflow. When pronouncing N the air flows through your nose. When pronouncing L, it flows past the sides of your tongue.

Oh, and yeah, you have to raise the center of your tongue for N. Otherwise the air just won't come out of your nose. I've just tried. It really doesn't work without raising the center of your tongue. The same goes for plosives. For all those sounds, your tongue seems to act as sort of an air dam.

In American English (at least in the Midwest) the tip of the tongue is more behind the teeth for the letter 'L' while for the letter 'N' it is on the alveolar ridge.

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Agreed Entbark, the OP's post is backwards for a midwestern accent.