One way is to use a flame maple veneer. This is a thin layer of maple that has been cut from a tree that has a naturally curly or wavy grain. The veneer is then glued onto the top of the guitar body.
Another way to get a flame effect is to use a staining technique. This involves applying a stain to the maple top and then wiping it off in such a way that the stain only adheres to the pores in the wood. This creates a contrast between the light-colored wood fibers and the dark-colored pores, which gives the top a flame-like appearance.
Finally, you can also use a burning technique to get a flame effect. This involves using a torch to burn the surface of the maple top. This creates a charring effect that gives the top a dark, smoky appearance.