Start of with training Ranged, you can either train in Lumbridge on cows and loot the hides for cash or just train at some higher monsters. If you're killing higher monster you better just safespot something like Barbarians.
After you get like 20 Ranged, you should go to the Hill Giants and kill these for limpwurt root and/or big bones.
When you reach 40 Ranged you should've collected enough cash for a Green d'hide pure set and an Amulet of Power.
For the Melee training you want to start the Vampire Quest at Draynor Village. 1-20 Attack in 1 simple quest.
Since you get 20 Attack, get a mithril scimitar, and make your way to the men in Edgeville.
When you reach 15 Strength or higher you can also kill monks in the monastery next to Edgeville. These monks can heal you if you talk to them.
So for the Mage part, you should buy a Fire Staff and like 2k Air Runes and 1k Mind Runes in the Varrock magic shop or GE.
You can just go back to the Hill Giants if you want to make some cash while training mage, or just safest monsters like lesser demons, zombies or skeletons.
This is just a simple start. What stats I would recommend:
Attack: 40
Strenght: 60 +
Defence: 1
Range: 65 +
Prayer: 1 or 44 for Eagle Eye
Magic: 1 or 37 for teleports
These are minimal stats before pking.