Cześć - I think it must be one of the most popular words in Polish :)
It happens to contain some characteristic sounds (cz, ś, ć) that can be challenging for a beginner student. Below you can find my pronunciation tips :) Keep on practicing! Get this one, and you actually score 2 words: hi and bye :)
How about replacing cz with sz ?
You see, that's not that complicated and you've learned a new sound and a new word :)