You mentioned the following problems in pronunciation for Chinese native speakers below:

1) distinguishing between the r and l sounds

In Chinese, there is no clear distinction between /r/ and /l/. The sound commonly transcribed as "r" in Pinyin is a retroflex sound non-existent in English. Chinese native speakers tend to substitute Chinese retroflex Pinyin r for /r/ in English because of this.

2) distinguishing between the n and ng sounds
For speakers of Putonghua (Mandarin) as a first language in the northern and south western part of China, phonological discrimination between final /n/ and /ng/ should not be a problem because it is a common phonological feature in their language. In a couple of Chinese dialects of south eastern China, on the other hand, it is a problem because there is no difference between final /n/ and /ng/ in these dialects. When using Putonghua as a second language, these dialect speakers also have problems to pronounce these sounds appropriately.

3) knowing when to pronounce final consonants
There are no final consonants in Mandarin except for /n/ and /ng/. There are a number of other final consonants like -p, -k etc. in south eastern Chinese dialects like Cantonese, Wu (Shanghai, Zhejiang and parts of Fujian province) with a very soft articulation of them so that you almost cannot hear them.

4) understanding the difference between voiced and unvoiced consonants, such as k and g, p and b, and t and d
In Mandarin and in most south eastern Chinese dialects, there is no real opposition between voiced and non-voiced consonants. Instead, there is a basic opposition between between aspirated and non-aspirated consonants. Those sounds of Mandarin normally written t, k, and p in Pinyin are the aspirated counter-parts of their non-voiced opposites d, g,and b.

In all the 4 cases, these are problems due to interference from the native source language Chinese (L1) when learning and using the target language English (L2). In the case of (1) and (4), these are problems pertaining to interference from native Mandarin as well as a couple of certain Chinese dialects other than Mandarin; in the case of (2) and (3), they are problems of interference for native speaker of non-Mandarin Chinese dialects.

I hope that these notes are of some help.