If Japanese natives struggle to undersatnd what you say, it may be because of your intonation. I will explain what intonation is and how to improve it for better communication.
Japanese is a language with pitch accenta and practicing the 4 patterns of accents can improve your Japanese dramatically.
Pronunication of Hiragana is the basis of speaking Japanese. This post gives you a complete chart of Hiragana with audio to help self-learners.
As a native Japanese speaker, I found quite a few differences in pronunciation rules between Japanese and English. Check out the 9 rules I'm explaining in this post to improve your Japanese!
I have to say pronunciation is so important to communicate in Japanese based on my experience as a native-Japanese who learnt English as a second language. And here is my learning guide.