What exactly are we trying to achieve here? More specific goals are easier to achieve, but more general-sounding goals like "justice" or "true democracy" tend to gather a wider tent of support.
Who doesn't want "justice"?
Who exactly has the power or resources to give us or help us achieve the goal we are trying to achieve? A government, a majority of the population?
The answer to this tells us the audience we will need to address our demands to.
This issue we want to talk about, who exactly does it affect on an everyday basis? These are the people most likely to be interested in what you are talking about. Identifying this groups is very important.
You have to assume there will be people against you. Even if it's about "justice". While theoretically everyone is for, some will know such a movement might weaken their own positions, and will covertly or openly work against it. Identify them.
Identify all those likely to be supportive of you, be it for ideological or even interest-based reasons.
For instance, a movement for female rights in country X can count on support from global feminist organizations, significant Western media etc.
Identify those who will likely not support you immediately, but might later become allies. Perhaps if they see you become popular or if those you address your demands to react overly negatively towards you. These are your "persuadables".
You want as few enemies and people actively working against you as possible. So identify those who, even if you can't count on their support, can be kept neutral and think about how to keep them that way.
You have to look into all the possible motivating arguments you have in your hand to get people from supporting you purely verbally to doing so actively, even if just on social media, which is already a lot.
What do we have? Money? People? Organizers? Popularity? What do we lack?
What is our message?
The message needs to fit into a clear story we can tell about the issue. Keep it short, keep it memorable, keep it emotive.
Are we going for shaming, supportive, educational, confrontational or what?
Timing is important. You need to pick a moment when your message might resonate most.
Location is important too. Protesting in front of your house will not get you much, in front of a parliament or during the speech of a president, different story.
What can go wrong? People don't respond. Police block our way. Rain. Police arrest us. People say our message is not new. Prepare strategies along lines of if X happens, we will do Y.
Good luck and have a nice day😃!