Dissertation writing is indeed one type of formal writing, which means the tone and the format of the whole paper should be something out of the ordinary. A dissertation is expected to be professionally made.

Apparently though, there are still some who commits mistake in writing. One of the common mistakes is wrong usage of terms and phrases. In that note, below are some of these terms and phrases that shouldn't be used in dissertation writing.

Adverbs. These words are often overly used. Instead of using too much adverbs, it would be better to use strong words instead.

Jokes. A formal document has no room for these. So better use it in your other works, perhaps on your literary pieces.

Perfect. People know that there's no such thing. So better not use it anyway.

Soon. In a formal document, you have to be specific especially if you're talking about time. Be concrete.