Do I need to send diplomas with my application?
No, unless they are specifically requested in the job ad. An application consists of a CV and a covering letter, except otherwise stated.
Should I supply references, letters of recommendation or proof of good conduct?The need for references depends on the situation. Referees will be contacted if the employer is uncertain or if a high level of professionalism is needed, for example in managerial or academic posts. References may be from former employers or colleagues (they are expected to answer a possible request for a reference from the employer).
A letter of recommendation can be useful. A good recommendation is always helpful. If you wish to work with children or the elderly, or in the financial sector, proof of good conduct is needed.