"g" in Mandarin Chinese is pronounced without the vibration of the vocal cords. In other words, it is voiceless and its pronunciation is similar to k in skill in English.
However, since voiced g does not exist in Mandarin, even if is mispronounced as a voiced consonant, it would not change the meaning of the character represented by the pinyin.
"k" in Mandarin Chinese is similar to k in English. It is pronounced with air flowing through the mouth.
"l" in Mandarin Chinese is similar to its English counterpart. However, the position of the tongue is slightly different when its English counterpart is pronounced.
When "l" in Mandarin is pronounced, the position of the tongue is the same as when "d," "t" or "n" in Mandarin is pronounced. That is, the tip or the blade of the tongue should touch the teeth or the upper edge of the teeth.
"er" is pronounced in a similar way to "e" with the tip of the tongue curled up.
"er" is not combined with any initial to be the pronunciation of any character.
ēr, ér, ěr, èr.
"ai" in Mandarin can be considered the same as eye in American English.
bāi, bái, bǎi, bài.
"ei" in Mandarin can be considered the same as the vowel in day in American English.
fēi, féi, fěi, fèi.
"uei" in Mandarin is the combination of "u" and "ei." Therefore, its pronunciation can be considered the same as way in American English.
wēi, wéi, wěi, wèi.
When "uei" is combined with another initial, "u" is dropped in its spelling. But this should not affect the way "uei" is pronounced. The "u" sound should still be pronounced.
guī, guí, guǐ, guì.
"uen" in Mandarin is the combination of "u" and "en."
Since "uen" is written as "wen," it should be cautioned that "wen" in Mandarin is not pronounced the same way as its counterpart in English such as wen in Wendy.
When pronouncing "wen," keep in mind that "e" in Mandarin is pronounced like uh in duh.
wēn, wén, wěn, wèn.
When "uen" is combined with another initial, the spelling is reduced to "un." But this should not affect the way "uen" is pronounced. The lips should be rounded (puckered up) to pronounce "u."
dūn, dún, dǔn, dùn,
hūn, hún, hǔn, hùn.