This tip deals with the word-initial sequence <poly>.
The list below contains examples of words where the first syllable bears the main stress. The pronunciation of the sequence is ˈpɒli.
polychrome polyglot polygon polygraph polymath polymer polymerase¹ polysyllable² polythene
In the second list there are examples where the first syllable bears a secondary stress and the pronunciation is ˌpɒli.
polyester³ Polynesia polynomial polyphonic polypropylene polystyrene polysyllabic polytechnic polyunsaturated
Finally, here are some examples of words where the second syllable bears the main stress and the pronunciation is pəˈlɪ.
polygamist polygamous polygamy polygonal polyphony
¹ Main stress on second syllable also possible
² Main stress on third syllable also possible
³ Main stress on first syllable also possible
With thanks to Alex Rotatori for comments