Do I need to send diplomas with my application?Not unless asked specifically to do so. However, candidates should have all the necessary documents (diplomas, certificates, letters relating to job experience) available and validated for when they meet the recruiter.
Should I supply references, letters of recommendation or proof of good conduct?
It depends on the employer. These are not normally needed, but a previous employer could be a referee. They are expected to strengthen the applicant's position by confirming the quality and skills of the applicant.
Letters of recommendation are not usually required, but must be available at any time. Proof of good conduct might be necessary for security and high-level jobs.