You go to light mountain which in on one island and find rocket brothers. You'll hear there password and they'll run away, go inside and then go up,left,right,down and you'll find ruby
How To Get The Ruby In Leaf Green?
In the northwest of mt.ember.. Where the two rocket grunts are. . They will move after you win them in a battle.. Go inside the cavern and you can get the ruby in the center of the cave. .
Go to two island and go to the cape brink on the north side. Bring her a Charzard, Venasuar, and Blastoise. She will teach a convenient to each. Then she will reveal a passage. Go foward left down then right and finnally up