I wonder what sounds other people tend to find difficult in Chinese. I am trying to improve my weak spots so had been thinking about it this morning.
For me I think the main ones are:
→ ju- sounds → 局
→ “c” /“ts” sounds - e.g. cao3 草， cai4 菜
→ qu/chu → 去/出 still gets me sometimes but I think this is laziness rather than actual confusion on how to say it
What about you guys?
I would love to hear how would LTL teachers answer this question. Also, if they noticed any patterns in accent and pronunciation based on students’ native language.
I have problems with z - zh, c - ch, s - sh when they come one after another, basically any combination with and without “h” sound.
I can pronounce them individually and OK with it if they don’t appear one after another but if they appear together it’s a problem like 十四，壽司，總是，從事 etc it’s better when the initials are different but when the initials are the same for sure I’d pronounce them wrong and I knew it as the words come out of my mouth but I still can’t control it.
Intonation. The hard part isn’t pronouncing the tone for an isolated syllable - but what I find difficult is to get the right “tune” for a sentence as a whole, and to fit the tones for individual syllables into that.
It would be great to have a class that focused purely on that, in fact…but I guess that’s the kind of thing that can be done in a 1-to-1 class!
Before we came to China for the first time, an extended Chinese course was actually part of my husband’s job training. I stil thank those teachers that for the first two weeks of that course we did nothing else but practice the differences of j/zh, x/sh, q/ch and the like. I do think that gives me an advantage learning new words… at least in Putonghua. Still remember the first time at the market and the lady coming from Southern China wanted 44 kuai from me and I was like 
.
PS: Totally had to edit as I just remembered struggling with a certain syllable! I keep pronouncing the E in 可以/可乐 too much like the German E instead of the schwa-sound that it’s supposed to be. Just can’t help it.
I could never say first and the second tone. Such a nightmare. Felt like my throat was getting twisted.
It’s ok now, but took me about a decade…
I always have a difficult time pronouncing 吃 chī and 车 chē, I don’t know why but I have to focus really hard to make it sound different!
And as many other students, I am struggling with the j / q prononciation too.
Likewise still never felt 100% comfortable with 去/出 and generally get by with the context of the situation!
My problem was the 4th tone, it always got critisized. Until an online friend told me to exaggerate and start the tone from high in the sky. Once an LTL teacher told me to take more care about the 轻声 and taught me how。So I think she was content enough with the others. 
The 1st tone is what I do in my classical singing all the time. it is my favourite, I immediately loved to pronounce 衣服。
the third tone is a perfect exercise to feel my vocal chords, the second tone always felt natural.
Next thing is to learn more about the changes in tone pairs, and to find the melody and correct stresses for whole sentences. I have recently started to go through the Standard Course books. Good material for sentence intonation.
In my early days of learning Mandarin, a language partner tried to teach me how to say Autonomous Region of Tibet. If you learn how to say that you should be good with all those nasty sounds!
西藏自治区
Xīzàng zìzhìqū
Have fun
That’s always been the toughest for me too. Especially 2 4th tones in a row. Hardest of all for me（has been/was) two 4th tones in a row with two difficult initials: ie. 介绍，照相.
Also the combination of four-three ie. 进口，驾驶
Tone wise, my worst by far is 2nd tone + 3rd tone. Trying to put some work with tone pair practice in order to make it better now - my mind knows what it needs to do, but it doesn’t come out 