Where can you find Zangoose

Zangoose is a normal type pokemon. But he is a really strong pokemon. With him I defeated the gym leader in Fortree city but against Altaria I used Gyarados .You can find Zangoose in route no 114 ( only ruby).

Where can you find Shiftry

Shiftry's lowest evolution that is Seedot. Seedot evolves into Nuzzleaf at lv 14. And you need to find a leaf stone. Okay to find a leaf stone remember the battle against May near Fortree city , you remind yourself to go down not up. Then surf and go down the stream don't stop until you see a poke ball and there it is a leaf stone.

Where can you find Absol

With the help of Absol I defeated the psychic gym very easily. Absol's dark ball was really useful to me at that time. You can find him near Fortree city but it is very hard to find him.But Absol is a very unique pokemon.

where can you find Aggron

You can find in the cave of Dewfard. To train Aron is really easy get him to lv 42 and he will become Aggron. But at lv 32 Aron will become  Lairon. They are all steel & rock type.

Where can you get Gyarados

You can get Gyarados anywhere near Dewfard as Magikarp you need it to get it to level 20 it is really hard to train as Magikarp but once you've trained it it is a very useful pokemon. And you will need it to defeat the sky gym battle in Fortree city.

Best pokemon team in ruby,emerald,sapphire

If you want a perfect team to beat the elite 4 you will need these pokemon
1 Blaziken
2 Gyarados
3 Absol
4 Agron
5 Shiftry
6 Zangoose

Starter Pokemon in ruby, emerald, sapphire

I know how hard it is to choose your starter pokemon is really tough. But if your going to choose in ruby,emerald&sapphire. I think you should go with Torchic or Mudkip. I chosed Torchic it was really easy to defeat the elite four with Torchic's evolved form Blaziken really easily. But if you chosed Torchic you will have difficulty on your 3 gym. But if you chosed Mudkip you will have difficulty in the 5 gym against Norman So, I suggest you pick Torchic or Mudkip