You have to get all the badges and all the HMs before you can get to the victory road, then to get through the victory road, you need to take the ladders that you havent taken before, so make notes and memorise which ones you have been through.
Sorry I cant be of more help, I started a new game and forgotten how to properly get through there.
Go to http://www.gamefaqs.com/portable/gbadvance/file/918916/47853 and there will be a map to help you.
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You need to get all 8 gym badges and you need a Pokemon that knows surf and maybe cut in your party. Victory road is to the left of viridian town.
oh please you have to get a green shard then give it to some guy poacifdlog
to obtain 5,ooo exp in Pokemon leaf green is to put a expirance share on the Pokemon you are training (best place to train is Pokemon league or victory road or clearun cave)
i herd you can find it in victory road. But i checked and it's a voltorb like in Pokemon blue yellow red And the not finished version Pokemon green. just kidding I'm not sur if its there or not I will check.
you can get it through Pokemon fire red or leaf green but if you complete the game you can get charmander from prof.oak in pallet town.