The following are some tips to earn some easy money:

(1) Through mining

-PART 1-
Get your mining level to lv115 1st,
If your going for the easy way,
Get your mining level to 60 (mine only irons)
You'll have about 7822 iron ores
You can sell your iron ores for 100gp each and that'll earn you around 770k-800k

-PART 2-
If you're going for the tougher task,
Like in part 1,get your mining to 15 but after 30 start to mine coals
From my calculation:
The iron ores between level 15-30 + coals between lv30-60 will let u make this amount : 780k to 950k (If u sell the iron ores for 100gp each and coal for 150-180gp each)

Notes: Remember to change your pickaxe whenever the requirements hits, this'll help a lot as the speed for getting ores will be faster..
Notes: As you get to level 60 mining, you can go ahead n proceed to the mining guild to get more ores...
Notes: Smithing wont be so much of earning when it's below 70, after 70 you can make more then 20k at once easily...

-PART 3-
You can also earn easy money through ores but u need starting money, just around 100k will do..
All u have to do is to buy coal(example) 100-120gp each from people and sell it at a higher price (example:150gp each for 1-500 coals,180gp each if u have tons of coals)

(2)Through Magic

-PART 1-
The best way for making money in magic perhaps is through runecrafting...
The higher the level of runecrafting, the more money you'll obtain...
For starters: The Best way is to runecraft air runes...
Air altar is located outside south of the entrance to falador and a bank is near.
You can try to sell the air runes for 15-20gp each which most of the rich guy buy them at...
-PART 2 & PART 3-(Tips tat need a lot of money)
2nd way is to get a capital of at least 220k..
All u need to do is stay in the runes shop and buy runes
Buy chaos and death runes and proceed to world with a larger population to sell your runes (chaos 120-150gp each, death-260-300gp each)
REQUIREMENTS FOR PART 3: Level 55 magic level
This tip also requires money because you'll be buying rune med for high level alchemy
Buy rune med from player 10k each and nature rune 200-300gp each
After high level alchemy you'll obtain 11520gp,you will get 1220 or 1320gp more profit for each high level alchemy