Before you set out to this mission's starting point, make sure that Michael is wearing a suit (this is requisite, e.g. if you haven't changed since the completion of the previous mission). Fortunately, you do not need to go shopping because it is enough to return to Michael's estate and open the wardrobe to choose one of the suits. The point that you need to get to is the garment plant in the La Mesa district that serves as Lester's command center. Once you get here, talk to Lester to learn about the idea to rob a local jewel store - Vangelico.