Every project starts with some kind of planning. It can be very simple or it can become complex as hell.
But there will be a plan – no plan, no project.
There’s no reputable consulting firm that won’t present you with a macro plan before you buy a project, and it’s great they do it.
Now… keep this in mind:
Perfect approach: Know the client, know the situation, create a plan, execute it.
Real-world approach: Know a little about the client, know even less about the situation, create a crappy plan, execute it, update to a less crappier plan, execute it, and so on. This is how it works!