[ezl]

if there's question about pronunciation, i find that putonghua (mandarin) educational material is very good and there are lots of references with clear pictures of what your mouth and tongue should be doing when pronouncing that make it just about impossible to make the wrong sounds (it won't fix your tones though).

it's difficult to describe and people pronounce english words differently so this isn't definitive, but

yao1 is like "yao ming", like if you stub your toe and say "owww!" in pain, or "yowzers!" -- those vowel sounds are all the same for me, so if they are for you too, that's probably the standard sound for "yao" in chinese.

liu4 is much more closed mouth. rather than opening your mouth wide, your mouth will be closed as if you are pronouncing the english name of the letter "e". the vowel sounds are roughly like taking the words "he" and "who", stripping the "h" sounds, and ramming the vowel sounds together. this (for me) sounds similar to the sound a child makes when he/she sees something disgusting and says "Ewwww!" or the english word "few" (the opposite of many). hopefully those 3 also sound the same to you.