By getting the Mystic Ticket (Acces to Navel rock for Lugia and Ho-oh, Island 8) or Aurora Ticket (Acces to Birth Island for Deoxys, Island 9), both are found at various Nintendo Events.
After this you can mix records or use mystery gift to get this from friends or give it to them.
first go make sure you have visited the gameroom on island 2. then go back to island 3 and you will be able to fight the bikers.
you go to an island and it is there. i think it is the 8th island.
Cinnabar island
The Pokemon day care for Pokemon Leafgreen/Firered is on island 4. You have to beat the elite 4 and get the machine on island 1 working to go there.
Go to birth island.
First go to six island
you have to get a rainbow pass
go to 8 island and find aten and he will take you there
go to six island and search in the grass. they are common
Team rocket will go to the dotted hole after five island in leafgreen, but I'm not sure about firered.
Surf south off of 5 island. Go past the island of flying Pokemon trainers. Memorial pillar right after.
to get to ruin valley on Pokemon leafgreen you have to get the ruby in mt. Ember and bring it back to celio then go to six island