I have been using the INFORM model to manage my project stakeholders for years now, and it’s a useful framework to ensure you cover everything that’s required to make project communication go smoothly.  The steps are:

Identify
Who are the stakeholders on your project?  A stakeholder is anyone who has a vested interest in the project – someone who wants it to succeed but equally someone who doesn’t.  You can't start managing stakeholders until you know who they are.  Who are the main groups or departments affected by your project?  Stakeholders can also be external to your organisation like the government and third party providers as well.  The identification exercise shouldn’t be done in a vacuum: you won’t be able to complete the list yourself, so get your project team involved too.

Nominate
In each groups you have identified pick someone to be the key individual. Choose carefully!  You may find that key people nominate themselves, which makes your role easier: it is better to work with people who want to be involved than those who you have to drag into the project.  Your key, nominated stakeholders should ideally be people who are directly affected, with enough authority to make decisions about things that touch their departments.  They are the person who you will use to channel communication back to their group.

Feel
Begin to analyse the attitudes of the people who have been identified as your key stakeholders:  those named individuals who represent each stakeholder group.  Contact them and explain about the project.  Get them onboard and coming to project meetings if necessary.  All this will help you understand how they feel about the work you are doing.  Do they support the project?  Or would they rather it was stopped now?  Are they ambivalent?  This group can often be the hardest to manage effectively.  Your initial stakeholder analysis is now complete.

Observe
Having established where your key stakeholders sit in relation to the project you can start to influence their attitudes.  The aim is to watch people over time, and help them move towards a positive way of thinking: a way that will help you achieve your aims.  Keep a close eye on people as their opinions will swing between positive and negative over the life of a project.  A one-off analysis exercise is never enough: you have to continually monitor how people are reacting and manage accordingly.

Review
People and job roles change.  So do projects.  The person who put themselves forward to represent the marketing team six months ago may not be the right person today.  If you notice that their influence is slipping away, or they are less inclined to come to meetings or respond to emails, then ask them if they still want to be involved.  If they say no, they could suggest someone else who would be a relevant addition to the team.  Make sure you brief any new stakeholder representative on their roles and responsibilities, decisions in the pipeline and what decisions you will expect of them in future.

Manage
The last step is to monitor and manage your stakeholders and their expectations as the project progresses - not just at the outset and when you need something from them.  Put a note in your diary to give your key stakeholder representatives a quick call every now and then just to keep them up to date.  This will help promote the project and also ensure the stakeholder concerned is mindful of the work being done.  It can also help build your reputation as an excellent project manager!  At the end of the project, thank them and manage them out of the team.  You want a good relationship with them, that could last over many projects, but you don’t want to be their personal helpline six months after the project has finished, so make sure they know who now has operational responsibility now the project has closed.