This is a very interesting question because it has many, many answers and very few generalized conclusions. The concept of a 'guerrilla group' is very broad. This can range from ancient rebellions using asymmetrical tactics to terrorist groups using urban guerrilla warfare in the 1970s. Within this wide array of organizations, groups, and factions are also a wide diversity in command structure, recruiting processes, and rules. Some guerrilla groups were affiliated with conventional forces or part of a conventional framework (and sometime even command), such as the French resistance or the Soviet partisans during the Second World War, and the People's Liberation Armed Forces (more known by the pejorative Viet Cong in the West) during the Vietnam War. This does not necessarily mean that they followed command structures and recruiting processes like conventional armies, but it is good to keep in mind that there could be an overlap. Furthermore, other important factors are shaped by ideology, improvisations in the field, or even desperation during that darkest hour. Each group, each organization, has to be considered within its own specific context. Although they might look similar on the surface, it is paramount for any researcher to dispel broad generalizations.

So, if we're going to make sense out of all this, I feel like should examine a specific example. The example I have chosen to answer your question is the armed wing of the National Liberation Front (Front de libération nationale, the FLN), the National Liberation Army (Armée de libération nationale, the ALN) during the Algerian War (1954-1962). I have chosen this example because the ALN is a prime example of a Cold War guerrilla force, resorting exclusively to guerrilla warfare and wasn't tied to a specific external nation unlike many other insurgencies during the same era, most famously the PLAF during the Vietnam War. Furthermore, the case of the ALN also shows the many intricacies that guerrilla groups often experienced.

Command and structure

The FLN was initially formed by men who were disillusioned by the infighting and political choices made by other Algerian nationalist organizations, like the Movement for the Triumph of Democratic Liberties (MTLD). The nine initial leaders of the FLN were all committed to national armed insurrection, something that would take place only months after the organization was first formed. Command structures, like the dividing of Algeria into different zones (wilayas) with a specific commander tied to it, were already in place before the first shot was fired.

As anyone can probably imagine, a national insurrection is going to take a little more than a few months to plan out properly. The start of the insurrection on November 1st 1954 was met with heavy repression, confusion on both sides, and passivity amongst the Algerian civilians who at this stage refrain from supporting the insurgents due to recent memories (such as the 1945 Sétif massacre) of violence committed by the French state upon civilians. Furthermore, as the war progressed, the lack of coordination between different wilayas became very clear. It was not a good start for the FLN.

In fact, it would take until 1956 Soummam conference for the FLN to start fixing these problems. For the first time was a document presented that laid out the organization, the political and military objectives and strategies, as well as the principles and policies of the FLN as a whole. More relevant for us are the clarifications of structures and guidelines. As historian Martin Evans explains, the Sommumam conference

[...] established the civil structures that would govern the military, appointing political commissaries to organize the population, advising on military strategy, and putting in place people's assemblies: a counter-state replacing French law and authority. The army itself was then divided into six zones (wilayas), themselves each made up of sub-zones (mintaqa), regions (nahia) and sectors (kism). Algiers meanwhile was made into an autonomous zone. In terms of fighting units the ALN was based on the principles of a strict military hierarchy [...] Soummam also defined the rules of engagement.

^- ^Algeria: ^France's ^Undeclared ^War ^by ^Martin ^Evans, ^pp. ^179.

Here, the ALN was formally born with a strict military hierarchy in accordance to conventional military hierarchies with a specific rank structure. These instructions and guidelines were heard and spread by the wilaya commanders present at the conference, but also through "tracts and the clandestine press" in the words of Evans. On the surface, this looks fine and tightly coordinated. However, deep political in-fighting within the FLN made the situation more volatile and unpredictable. Furthermore, some leaders were arrested or captured by the French state. For some, however, arrest was a blessing in disguise since they their reputations were untainted by the internal controversies caused by the FLN during the war years.

Additionally, we should also consider the fact that these instructions weren't always followed. There was still no unified wilaya coordination and individual wilaya commanders were often left autonomous. Nowhere is this more evident than in the question of women fighters in the ALN. Some wilaya commanders gave strict orders not to recruit women and stressed the traditional, unequal role of women in Algerian society. Yet this did not necessarily mean that these orders were followed and women who were fighters before the orders were announced continued to be part of the ALN ranks while new women joined them.

Ultimately, the French never took noticed of the power struggles and infighting within the FLN. If they had taken advantage of it, things might have turned out differently.

Recruitment and laws

We've already spoken very briefly about the recruit of women into the ALN, which in my opinion is a perfect example of the complexities of recruitment during this conflict. As mentioned before, the seed of the FLN laid in the MTLD. In turn, the equivalent of the ALN in the MTLD was Special Organisation (OS). Although disbanded in 1951, the FLN would draw upon the OS network to recruit members for their insurrection. Many FLN leaders had been members in the OS. Clearly, however, an organization that had been defunct for three years would not produce recruits forever.

The limitations brought upon the ALN after the initial insurrection meant that careful vetting of potential recruits was in order. The ALN didn't just take anyone. A strict sense of security was paramount to avoid infiltrators and other potential saboteurs who could lead to the destruction of these often small units. Yet it wasn't only based on suspicion. The ALN had to be selective due to its nature of being a rag-tag guerrilla force. Unlike the PLAF during the Vietnam War, the ALN did not have a steady supply of the latest weapons, uniforms, food, and medicine. That meant having to only recruit a limited number of men and women based on local networks. In the long run, this would create issues when the potential recruits weren't just from the immediate rural surroundings but also from the cities. These students, some with invaluable skills in medicine (that historian Jennifer Johnson discusses in-depth in her book The Battle for Algeria: Sovereignty, Health Care, and Humanitarianism), were seen with suspicion by rural commanders. These tension are very interesting to look at, but more research needs to be done within that subject. An additional aspect that is often forgotten in the context of guerrilla forces is forced recruitment, something that the ALN also resorted to in some cases. The clandestine nature of guerrilla warfare caused a great deal of suspicion, something which prompted excessive control by commanders over their soldiers which in turn disillusioned fighters who were already in a troublesome situation due to the lack of practically everything in the ALN. Returning to the topic of women, one strong reason for the segregation of women from men (and thus deny women a place in the ALN) was the ever-present need by the male commanders to control female sexuality.

Finally, we turn to the justice system in the ALN. With the background of the ALN as always being in a dire situation, with limited supplies, the constant need for control and the ever-present suspicion, one shouldn't be surprised of the lack of finesse in the ALN justice system. Crimes such as disobedience and desertion, as well as any serious form of disobedience would ultimately result in execution of the person found guilty of that crime. It is very telling of the nature of control and obedience that took a central place in the ALN that all forms of disloyalty received the most severe punishment otherwise reserved for murder and rape.

Sources:

A short and academic overview of the ALN can be found in Jacques Frémeaux's chapter, National Liberation, Algerian 'Style'?, in Insurgencies and COunterinsurgencyes: National Styles and Strategic Cultures by Beatrice Heuser and Eitan Shamir (ed.) (Cambridge University Press, 2016).

Algeria: France's Undeclared War by Martin Evans (Oxford University Press, 2012)

A Savage War of Peace - Algeria 1954-1962 by Alistair Horne (Macmillan, 1977).

The Battle for Algeria: Sovereignty, Health Care, and Humanitarianism by Jennifer Johnson (University of Pennsylvania Press, 2015).