Often times it is not a pronunciation error that confuses a listener, but an error of syllable stress. I recall a time a client came late to class exasperated. He had just come from trying to buy something at the grocery store, and wanted to understand why the employee could not understand him when he asked for help locating the item.
As he was in a hurry, he asked the first employee he saw for help to locate the item. This happened to be someone in the produce department. My client wanted to know where to find the CAsettes. (Yes, this was a looong time ago!)
So there were 2 issues complicating this communication. First, the employee probably thought he was looking for something in the produce department. Second, my client emphasized the first, rather than the second syllable in cassETTE.
There are numerous rules for helping speakers to know where to put the emphasis in a word. Native speakers know from the process of listening as they learn the language during their formative years, and the brain learns to intuit most of these rules. Adult non-native speakers usually need assistance to utilize the rules correctly. Although the rules are taught in our PRISM program, it requires improved listening skills to integrate these into conversation.
Because my clients are already fluent in American English, many of these errors are habitual. Through identifying their high frequency errors, and having clients record and review themselves in conversation, they learn to recognize these errors and correct them.
English has lots of suffixes. Some suffixes are usually emphasized, some require emphasis on the syllable prior to the suffix, and some on the syllable that are two syllables prior to the suffix. Some suffixes have no influence of where the syllables emphasis occurs.
A few examples of how words change with suffixes.
ENgine --- enginEER GRAduate --- graduAtion SIGnify --- sigNIFicance
Angel --- anGELic CLINic --- cliNIcian
I have included a link to a good website that shows the various suffixes and how they impact where the syllable emphasis goes. I hope you find this beneficial.