geezerguy

To be able to trade from Ruby to FR and LG you need to beat the Elite Four in FR/LG and then obtain the National Dex from Professor Oak. Now. Head to One Island and talk to Celio in the Pokemon Center(The guy next to the massive machine) and he will say he needs help with it, after he says this surf to Mt. Ember you should find a cave with two Rockets outside of it who will be talking and give out a password for their warehouse on Five Island, which you can't access yet. You need to fight these to get in, which isn't that much of a challenge. In the cave you'll find a Ruby, after obtaining this go back to Celio and give him it, he will then give you a Rainbow Pass. Now, you'll be able to access Four, Five, Six and Seven Island. Go to Four Island and go into Icefall Cave, where you will encounter Lorelei having trouble with some Rockets, after you've dealt with them you'll get the second password for the warehouse from them. After this, go to Six Island and enter the Ruins by cutting down the door to it, in this place you'll find the second gem you'll need, the sapphire, but then a Rocket/Scientist will steal it from you and you have to get it back.

So, go to Five Island and find the Rocket Warehouse, and the passwords will be entered and you'll get in, they'll be quite a lot of Rockets to battle outside and in, so be prepared. At the end of this warehouse you'll get the sapphire back. Give this to Celio and after this you will be able to trade from R/S/E to FR/LG!

Hope this helps,
~Geezerguy.