Well, I'm not sure about LeafGreen but it should be the same as FireRed. I can't remember it to well, so go to the PokeDream site:
http://pokedream.com/games/fireleaf/walkthrough/17-island1_2.php#island4
There is a list on the left hand side that will help you get to all seven islands. I just did everything it said.
Hope this helps.
actually there are seven
You can't go to Hoenn on leafgreen, but after you beat the elite four you can trade with hoenn and go to the sevii islands. (all seven of them)
The same way as fire red!
The seven islands are part of sevii island that have the trainer tower and tanoby ruins ,tanoby key and there is the secret room and you can catch unown there
first get them on firered/leafgreen from the seven islands, then migrate them
You find the ruby and give it to celio
you need to fix that professors machine on the sevii islands (the seven islands) the ones that you unlock after the league
8 Island does not exist. Only the sevii islands. There are seven islands in leafgreen and firered. Four of them can only be visited after finishing the game.
There is no island 9 in either Pokemon FireRed or LeafGreen. Whoever told you this is very off. There are Seven Islands (Sevii Islands)
Use vs seeker and train at six/seven islands, maybe......
Johto is inaccessible on Leaf Green although Islands Four to Seven contain Johto Pokemon.
On Seafoam Islands.