How can you avoid plagiarism?

One essential rule :

You must ALWAYS cite the source where you found the elements used (extracts from texts or ideas, arguments, illustrations, analyses, etc.) and clearly indicate what exactly you borrowed.

The referencing rules vary according to the field (make sure you apply those that relate to your section/faculty).

Nevertheless :

Your sources must always be cited clearly and in full

• If you insert an extract from a text (quotation) in your work, you must place it between brackets and give the complete reference (author, source, pages, year), whatever the medium, or the original language or the length of the extract used. It isn't sufficient to use italics or bold. The brackets and the explicit and complete citation of the source are essential.
• If a document (part of or all of it) is paraphrased, or you insert an argument, analysis, image, diagram, results, etc., in your text, don't use brackets. Instead, you must cite the complete reference of the source.

Bear in mind that even if you cite the reference of a document in the general bibliography at the end of the work, you still have to mention the borrowed material in the exact place in the text where this borrowed material is used, whether it is a textual or rephrased quotation.

In your references, you must include all the works you have used for your piece of work.

You can only include the documents that you have actually read. Therefore, make sure you cite the relevant reference! A few special cases concerning the author to be referenced (always together with dates, pages, publisher, etc.):

• If you are using the translation of a work in a foreign language: refer to the work actually used, i.e. the translation, specifying the translator's name (by putting Trad. or Trans., for instance).
• If you are using a quotation from X found in a work by Y: in the place where you are using the borrowed material, refer to X, specifying quoted by Y, and in the general bibliography, only refer to the work by Y (the only one you have read).
• You cannot identify the natural person who created the extract you are using: you must nevertheless mention this source. Depending on the referencing system, the first words of the reference (usually the title) and the year of publication will have to be quoted, or, in other systems, the word "anonymous". In other cases, the copyright owner may be an organization or institution that publishes the document, so it is appropriate to cite them.
  In any case, if you have no idea where certain information comes from, it is best to refrain from using this unverifiable source!

In these different cases, as elsewhere, the use of brackets is always compulsory for quotations.

Do not hesitate to consult the resources proposed at ULiège to know the rules in force in your discipline: