There are a few steps in the Team Magma Plan.
The first plan is to steal parts for a weather control device from the Devon Corporation. The plan is that they will try and ambush a Devon worker and blackmail him into stealing crucial device parts for them. If they succeed, they receive the parts from the worker. If they fail, they will try and steal the parts directly from the corporation by themselves.
The second plan is to secure rocket fuel. They need to rocket fuel because they need the fuel to power their specially designed tunnel that will dig them down towards Groudon. They will also use th fuel to blow up Mt. Chimney and cause a reaction to awaken Groudon. They raid the Mossdeep Space Center for the special fuel.
The third plan happens after the first and second plans are attempted (no matter if Team Magma was successful or not). They will attempt to kidnap a meteor scientist and have him unearth a powerful meteor with which they will use to make active the nearby volcano, causing it to erupt. Coincidentally this is done at the same time Team Aqua try and kidnap the same meteor scientist so they can get the meteorite to use its power to subdue the volcano instead of making it active. Team Magma will send Admin Courtney to kidnap the scientist.
The fourth plan is after the third plan. They steal the Red Orb from Mt. Pyre. They use the They begin digging into the volcano and using the Red Orb to guide them (it glows brighter as they dig towards Groudon). They will try to unleash Groudon and it's ability to dry up the waters to make more land. They will learn the error of their ways when Groudon proves to be too strong and is making things worse with its droughts.