A list of good ways of money making guides are listed at the runescape wiki.
There are many ways to make money. Soft Clay requires level 1 mining, a pick axe and a bucket (preferably four). Mine the clay south-west of Varrock, mix with water from Varrock fountain, store in varrock west bank and repeat.
A round trip take about 3 or 4 minutes and assuming prices are 208gp each for your soft clay, thats 5k per trip.
You could also cut different trees, mine rune essence, or even collect planks in the wilderness.