Managing stakeholders is primarily managing their expectations. And making that management efficient calls for starting early and with some degree of formality.
For example with a project, start with a project charter. Identify the objective(s), key players (stakeholders, including those who will do the project and others), roles, timeframe, budget (financial, people time, other resources), and deliverables. A key question to ask the stakeholders is "How will we know when we're done?" Review the charter (socialize it) with the stakeholders and formally confirm their agreement/buy-in. (That doesn't have to be signing in blood, but it should be explicit and clear.) Develop other elements -- resource plan, task list, risk matrix -- based on the charter. Then as the project proceeds, refer regularly to the charter and other elements to reaffirm that the project is indeed on track. With clear documents and a regular cadence, you should be able to manage expectations with efficient effort.
Interesting follow-up question. For stakeholders, consider anyone who has something to gain or lose (hopefully not really lose something, but perhaps contribute resources, or have a shift in influence). And for priorities consider how much gain they will enjoy, or loss they will suffer. I like to meet with the stakeholders both individually -- so I can read their feelings as well as judge their words -- and together, so that I can also see the group dynamics.
Khalil, if I may offer my opinion:
As a project progresses through different stages, it is quite conceivable that there may be newer parties who will become stakeholders and/or someone who was identified earlier as a low priority stakeholder in the 'inform' bucket may become a vital stakeholder who now has a major influencing force - positive or negative, due to changed circumstances. An ally may become a foe or vice-versa. An erstwhile key stakeholder may exit the scene or lose influence. These are just a few examples of changes that may occur in today's dynamic environment.
Hence stakeholder identification and prioritisation (as to who is in the inform bucket, who is in the consult bucket and who in the veto bucket) - both of these should be an ongoing process and be done dynamically.
Interesting dialogue. In my experience, the most important stakeholder might be the one you didn't include in your process. I teach a case study called "The Forgotten Stakeholder," detailing the consequences of one such process, where the client neglected to think broadly enough, and was blindsided by a stakeholder outside what they thought was the project's impact zone. So, in addition to John's definition of stakeholders as those who "have something to gain or lose," I suggest asking the question: "who else could possibly be impacted/stop us/help us?" and broaden your aperture, even if it feels artificial.
Following-up on Elisa's point, I would say follow the data. In this day and age, stakeholders leave a digital footprint through social media. The challenge is that the data is unstructured which by definition means that it lacks context. So how do you identify your key stakeholders or rather said, the unknown stakeholders when the information is unstructured? In our experience, first you need the ability to capture stakeholder data ( internal amd external) i.e Twitter, Instagram, Facebook, email, text docs, etc.
Once you have the data , you can run all types of analysis. We recommend using machine learning platforms to classify the data so that you add context and understand the issues of your key stakeholders at a granular level. A better understanding of stakeholder issues can help you address those issues in a more effective and proactive way. Ultimately this approach can help build stakeholder trust by enabling your organization to rapidly respond to stakeholder concerns.