Pronunciation
Sound–Letter mapping is the first pronunciation challenge you will encounter in many languages. A common practice to solve it is to make respelling notes for ambiguous or confusing words.
For instance, the word Wednesday can be phonetically respelled as wenz-dei to make it more clear that the first d is silent.
However, you need more than respelling when you want to represent sounds that are not in the language’s alphabet. For instance, you can’t indicate that the a in cat is not the same as the one in bath. And you will confuse the hell out of yourself if you respell cut as cat. This circumstance will, unfortunately, occur often.
IPA
A solution to this problem is to learn and use the International Phonetic Alphabet (IPA), a standard written representation of speech sounds. In IPA, each symbol unequivocally identifies one sound.
IPA is a good aid, for example, when you are not able to distinguish between 2 phonemes that are like day and night for natives. For instance, Italian learners might not realize that the double-z in the words pizza and mezzo are pronounced slightly differently. If you are not Italian, try to pronounce them yourself now, then check the correct answer:
pizza
audio from howtopronounce.com
mezzo
audio from howtopronounce.com
Can you tell the difference? The zz sounds like ts in pizza and like ds in mezzo. Perhaps you find it easy to differentiate them when you hear them back to back, but when you hear them in context it won’t be so easy. The good thing with IPA is that you don’t need to second-guess: /ˈpit.t͡sa/, /ˈmɛd.d͡zo/.
Other times, just one imperceptible difference is all that differentiates two words. This happens more frequently (from an English native speaker perspective) in tonal and pitch-accent languages, but there are examples to be found in many more languages.
For example, the Danish words hun (/hun/, she) and hund (/hun̰/, dog) are identical except for the ◌̰ in hund. The ◌̰ symbol denotes an abrupt interruption of airflow in the glottis. This feature (called stød in Danish) is ubiquitous in the entire language:
As an exercise, go through the sounds that exist in your mother tongue and observe how they are produced. Notice how the interplay between tongue, teeth, and lips can lead to radically different sounds. See what happens when you involve the nose, or when you push air from the back of your throat.
Equipped with this awareness you can now seek to understand better how to pronounce difficult sounds in your target language. When you do it, put your complete focus on sounds and forget about meaning.
Image from XKCD, by Randall Munroe. CC BY-NC 2.5