Make text lowercase, remove text in square brackets,remove links,remove punctuation and remove words containing numbers.
Removing the most occuring words.
Removing of rare words
Stemming is the process of reducing inflected (or sometimes derived) words to their word stem, base or root form.
Lemmatization is similar to stemming in reducing inflected words to their word stem but differs in the way that it makes sure the root word (also called as lemma) belongs to the language.