All those postnominals, those initials after ones name, do have meaning and are not just "chicken scratches" as they are often referred to by the uninitiated. Postnominals represent the achievements that one has obtained.
The most common types of postnominals seen are those for academic degrees. Academic degrees are listed from the most junior to the most senior after the name. These are in order the Associate degree, Bachelor, Master and Doctorate degree. Associate degrees are mainly of American origin; however, some Ontario and British Columbia institutions are awarding these degrees. By the way, degrees are not issued just by universities, but also by colleges and institutions, the most famous being the Massachusetts Institute of Technology.

Of note is that the degree of Medical Doctor (MD), Latin Medicinae Doctor, is an undergraduate (Bachelor level) degree in North America. British institutions issue a Bachelor of Medicine (MB), Latin Medicinae Baccalaureus, as well as a true doctorate in medicine equivalent in level to the Doctor of Philosophy (Ph.D), Latin Philosophiae Doctor. A dental degree is also an undergraduate degree.  This particularity results for those with MD or DDS postnominals listing graduate degrees of a Master of Science (MSc) or Master of Public Health (MPH) after a degree incorrectly interpreted as a doctorate! Although it may take several years to obtain and many could and do obtain additional degrees during their study, this is still an undergraduate degree without the thesis and dissertation required for a graduate degree.

The legal degree, Bachelor of Laws (LL.B.), Latin Legum Baccalaureus, is also an undergraduate degree; however, feeling pressure to be equated the same status as medical doctors, one sees the development in the United States of the undergraduate legal degree of Doctor of Justice, Latin Justitia Doctor.
Now this being said, the medical profession, as well as others such as accountants and engineers, have additional postnominals that are often listed. Fellow of the Royal College of Physicians and Surgeons (FRCPS), Charter Accountant (CA), and Professional Engineer (PEng) are a few. These are not issued by educational institutions but by professional bodies. However, these achievements require some form of additional study and examination, thus are considered as forms of academic degrees and listed like graduate degrees for ordering as postnominals. These additional professional designations are, as well, becoming more common for other professions, like nursing and education.

Academic qualifications listed as a certificate (Cert.) or diploma (Dip.) may also be listed. Usually these are junior and listed before a degree; however, one may obtain a diploma or certificate at the undergraduate or postgraduate level, leading to variance in ordering postnominals.

The most senior degree is that of a doctorate, seen often as the Doctor of Philosophy (Ph.D), Latin Philosophiae Doctor. Other areas of scholarship also have doctorate degrees, such as Doctor of Letters (Litt.D.), Latin Litteranum Doctor. The Doctor of Laws (LL.D.), Latin legum doctor, is usually given as an honourary degree. However, there are institutions that actually grant this formal degree.

Senior to academic degrees in listing of postnominals is active registrations. The well-known postnominal for a Registered Nurse (RN) is in this category, as would postnominals of our profession, EMT and EMT-P.
Registrations require active participation and thus may be lost, which give rise to the seniority of this category, listed before academic degrees.

The most senior category for listing of postnominals are those of honours for orders, decorations and medals. These are issued by governments, sovereigns and some private authorities. The specific order for listing these postnominals are usually outlined by the issuing authority, with those issued from one's own government first, then other governments and other authorities. The most noted postnominal in this category is that for the Victoria Cross (VC). British peerage knighthoods, for which Canadians are ineligible, are also in this category. The British Venerable Order of Saint John of Jerusalem grants knighthoods to Canadians. However, these do not create peerage. Canadians are also eligible to receive foreign and private knighthoods for these also do not create peerage.

For many the correct ordering of postnominals will be of little concern, listing only one or rarely moving in society where postnominals are in common usage. For others, correct ordering of their postnominals reflects on the completeness of knowledge in this area. One may list only  part of their postnominals to avoid confusion, with the Americans listing only the most senior degree. However in the true British tradition, all postnominals are listed. After one's name is first honours, then registrations, and last, academic degrees.