Often, you might want to express something simple. This often helps smooth your language skills and make you sound more fluent. These one word expressions can help you conversationalize in Japanese.
Yatta - Use whenever you feel victorious. Can replace "I did it!" or "Hurrah!"
Honto - Use to confirm what you just heard. Replaces "Really?"
A, so desu ka. - Used to say you get what you heard. Replaces "Oh, I see."
Mochiron - Used by confident people who are 100 percent confident of their opinion. Replaces "Of course!"
A, yokatta - Used to replace "What a relief" or "Oh, good" or even "Whew".
Zenzen - Used for denial. Replaces "Not at all" or "nah.."
Nani - A very common form of "what?" Use if you didn't hear or you didn't quite get what was just said.
Doshiyo - Use this if you are in a panic. Can replace "What do I do?" or probably even "Oh man, oh man, oh man...".
A, bikkurishita - Used when you're surprised. "What a surpise!"
Yappari - Used when you thought something might happen and it does. Replaces "I knew it!" or maybe even "I told you so."
Kawaii - Used when you consider something cute. Replaces "Oh, how cute!"