Countries such as France and Sweden had estate parliaments. In France, commoners (everyone outside of the nobility and church) made up the third estate, while in Sweden, these were divided into the 3rd and 4th estate. How did one attend these assemblies? I'm assuming there was farmers present, how were they picked? Was it simply first come first serve, or was there some kind of process already established?
The assembly was the Estates General; Versailles was the name of the palace where they met.
Representatives to the Estates General of 1789 were elected by their respective estates, rather more freely and more democratically than elections for many a decade following. There were specific procedures devised for this call of the Estates General, but I don't know what the methods were for 1614. There was intense interest in procedures: for example, a major issue had been having the third estate equal the other two together, and the exact boundaries of elections became an issue for a bit.
The procedures were rather complicated. (Quelle surprise: it was ancien régime France, after all.) There were some exceptions for Dauphiné, Navarre, and Brittany. Other than them, and provisions for 8 cities, there were 234 constituencies each electing 2 clerical, 2 noble, and 4 third-estate representatives, each chosen by their respective estates.
For the third estate, all male taxpayer over 25 had the right to attend a primary assembly. But that primary assembly simply elected 2 delegates for each 100 households. The delegates elected in a constituency met in a second-level assembly to elect their 4 representatives. (Future elections had wealth requirements for participation. Or tax requirements; as I recall, in the Directory men tried to get tax breaks for their opponents so as to kick them out of politics.) Clergy and nobles were eligible to be elected as representatives, but few were. Because of time and distance for the second-level assemblies, and more so for the Estates General, and because none of it was paid (only the heights/depths of the Revolution provided pay for anyone), men who didn't have money and leisure couldn't proceed even to the second level, like peasants and artisans. Those who bothered to vote (in Paris, participation only got up around 25%) had some education and leisure and voted for those like themselves. Those elected tended to be those used to public speaking, meetings, and laws. So about two-thirds of those elected were connected to the legal profession in some way: lawyers, notaries, or judges. Only some 85 representatives were connected with mercantile pursuits.
If you're curious: the electors for the first estate were all of the beneficed clergymen + representatives elected by monasteries and chapters. For the second estate, the electors were all the nobles who had full transmissible nobility. (There were various types of nobility adhering to various offices: some ennobled permanently and at once; some required several generations to trigger full inheritable nobility.)
Source: William Doyle, The Oxford History of the French Revolution, ch. 4.