Most of the people can’t appropriately balance their voice and intonation, that’s because of their unskilled tutors. Sometimes it’s better not to raise your voice and speak at a steady pace. The worst thing is to change your intonation too much without any necessity.
The other thing you should avoid is rising up your voice at the end of every sentence. You should start your conversation with a high tone then make it down at the end of your sentences.
The most effective way is to listen to interviews or movies or documentaries. You would hear appropriate native intonation there.
You can also repeat after every conversation you hear, then record it and see if it’s the same or not. Try to keep your mistakes in mind. Actually, you should imitate the sound, it helps a lot. It may seem not a great suggestion but you can easily moderate your voice with imitation.
If you have a native friend, you can practice with her/him; you will be able to reach an appropriate intonation for sure.
Recording and hearing might be a boring and long process, but you should wait and practice regularly. Intonation needs a lot of practices, so you should carefully practice every day.
A common mistake among who speak English fluently is the intonation. It makes people confused and they can hardly make people understand what they’re saying! They actually want to make up for their intonation with speaking at high speed. To improve your verbal communication you should speak more obviously.
Don’t merge words together and pronounce the hard words with short pauses.
Overall, every language has its own unique music and melody which is called intonation. If you want your speaking sounds like a native you should learn how to use appropriate intonation. Never ignore this part of the English language learning.