Wood cutting

You can make money from wood cutting at lvl1
Lvl1 Normal trees normal logs 30gp each or save for fletching fire making or construction.
Lvl15 Oak trees Oak logs 58gp or save for flething fire making or construction (best place to cut is at seers just outside the bank or west varrok)
Oak trees are by far the best money maker at low lvls
There is no money to be made with chopping willows or maples so only chop these if you want exp.
Lvl35 Teak trees Teak logs
Lvl50 Mahogany logs Mahogany logs
Lvl60 Yew trees yew logs 450gp each or keep for fletching , the best place for chopping yews is south of the flax field at seers (if fire making sell the yews and buy maples alot more exp per gp that way)
Yew trees are by far the best money maker at higher lvls
Lvl75 Magic trees mage logs 1.1k each The best way to cut this is to go to The grand tree area.There is a magic tree beside the tree farm plot.If you have a high enough lvl to plant trees plant the best tree you can, you can chop this as you wait for the magic tree to respawn or go to yews just north.
Magic trees are slow exp but a good money earner.
Lvl68 Clinging ivy 0gp but the chance of getting a birds nest. the best wood cutting exp in the game.

Farming

Farming is a great skill to make money at and you make money from lvl2 onwards. Never ever throw away any of your harvests as these can be used later on to pay the gardener to look after your plants.Prices shown here will be average prices as you know prices vary hour to hour.
Lvl2 Marigolds 3k each or keep for using with summoning.
Lvl15 Oak trees cut logs 58gp each or keep for fletching or construction.
Save all willow and maple logs for fleching or fire making as there is no money in them.
Lvl32 Rannar Herbs 9k each or save for making prayer pots
Lvl44 Irit Herbs 4k each or save for super attack pots
While waiting for crops to grow either cut wood or fire make.(on low lvl farming)
Use a fruit bat to make fruit for you near a lepricorn farmer and get him to turn the fruit into bank notes for you.