We don't really play class at all in the game I run.
Instead we use real world professions from the time period of the milieu. That's because in real terms the in-game designations for class don't really stand for classes at all, they stand for professions.
A class is really a rank in society, and since most D&D settings vaguely or directly reflect Medieval or proto-Medieval societies then classes are really a form of ranking in society (nobility, merchant, peasant, etc.), and usually a feudal type of ranking. Let's face it, if most players were of nobility or of a high class, then they would probably not be following a career as an adventure or explorer (unless they were not born early in family line) but would rather be pursuing a career in politics, administration, the clergy, or soldiering. Meaning that in reality most all characters are of middle to low class in their world, and so class is not really a consideration in actual fact, profession is.
Thus, so-called in-game classes are really not class at all, but professions. And usually very standardized and extremely general professions; fighter, wizard, cleric, and so forth, though with some very specific professional designations, such as Paladin or Ranger or Bard. Then again you have the proto-professions which are not really professions per se, but rather cultural types, such as the Barbarian or Monk. So the Barbarian is neither a class nor a profession, but a type.
So instead I let my players choose some profession, let's say, given our milieu, a Byzantine Solider, or a Mendicant Cleric. Then we use a system very similar to that employed by the US army as far as skill sets are concerned.
Most Soldiers will undergo basic training where they all receive a basic or preliminary instruction in a basic set of skills related to soldiering. Thereafter follows technical training, then professional training, and expertise.
So each player is allowed to choose a basic skill set for the character they create which relates to basic profession, say the Fighter. Fighter is just a general profession "type." From that point they may then pursue more advanced occupations which would lead them to becoming a professional soldier, a paladin, a ranger, etc. If a profession is really a subset of a progression form a more general profession, like from Fighter to Paladin, then the Paladin itself has a general set of professional skills, or so does a more advanced and better trained Soldier. Because not all Soldiers are alike, some are close combat fighters, some artillery-men, some tacticians, some infiltrators and scouts, some reconnaissance specialists, some mounted, some foot, some bowmen, etc. So although each profession and sub-profession has basic "skill sets" each individual is also free to pursue almost any skills that interest them personally.
So a cleric might want to learn systematic theology, and medicine, but he might also want to learn herbology, and animal husbandry (as was fairly common with some orders of Medieval monk), and he might also want to learn to box and wrestle. So each profession undergoes a basic skill set of basic training, but thereafter each individual may diverge in both his more advanced training, and in the course of pursuing his particular personal interests.
The class system serves only as a basic guide to adventuring profession "types." Thereafter players are allowed to design their characters pretty much as they desire and would be the real world case for the milieu in which they operate.
So we have a Byzantine solider from Nicea, a Paladin from the court of Charlemagne, a Bard from the British Isles, a Barbarian from Russia, a Roman Catholic Cleric from Ravenna, etc. Each is recognized by their cultural and professional backgrounds and basic training, but thereafter, as they have progressed each character has been allowed to pursue both more advanced professional training and personal interests. And often the players choose personal interests skills for their characters that fit their interests in real life, and/or skills and capabilities which allow each member of the party to specialize in some area of knowledge, expertise, or ability which is outside their normal skill set range, so the party as a whole can either overlap capabilities for mutual advantage, or develop capabilities to accommodate or compensate for normal professional deficits.
We also do not limit skill acquisition or development to already existing in-game skills. If players have some real world skill which they want translated into the game, and it is feasible for the milieu, then we create a skill to match player capabilities and interests. In that way the game reflects real life for the players and vice versa: the game becomes skills practice or exercise for real life skills (depending of course upon how individual adventures and scenarios are written and executed).
Then again we also have a special profession, the Vadder, who is more like a Renaissance adventurer, or Jack-of-All-Trades. This character does not choose a profession (the Vadder is not a real profession per se, but is rather an "adventuring type") but a certain skill set (or sets) which is almost immediately open to wide variation and the point is to develop a character who is extremely unique in nature and also able to do a little bit of everything, because the Vadder usually operates alone, as an independent agent, and therefore must possess a wide range of skills and capabilities, from survival to escape and evasion to manhunting and tracking to some combat to first aid and infiltration, etc.
That's the way we do it in my game.
