It's a job best left to professionals unless you've had some experience before. Metallics almost always comprise a base coat in addition to a clear lacquer top coat meant for that protection and added gloss. Thus you need to spray metal flake on top of a ground coat. However, some ground coats may be clear coated to obtain a sparkle and sheen of its own
Usually such sprays are water-based, that are sprayable, or even brushable strippable coating. You will need to apply the flakes evenly and ensure sufficient ventilation. Don't over-spray and go as per instructions given on your metal flake can so as to get the best result.
Try practicing spraying before attempting the actual job. It can be tedious so aim for a steady hand.
Usually such sprays are water-based, that are sprayable, or even brushable strippable coating. You will need to apply the flakes evenly and ensure sufficient ventilation. Don't over-spray and go as per instructions given on your metal flake can so as to get the best result.
Try practicing spraying before attempting the actual job. It can be tedious so aim for a steady hand.