Honestly I had a problem with this for a while but I make a goal for myself to make a chapter at least 1000 words long. Think of your scenes and the dialogue. Like the line and then the pose or environment around the character.
For example:
Inosuke cackles out, his chest buffed out as he lets the world know who he was.
“HAHAHAHAHAH I am the Great Lord Inosuke!”
Then honestly, practice practice practice