I started with high sec mining, and after a couple of weeks I could make about a million isk in 40 minutes with an Osprey and a Badger II.
Lately, I started running some missions since my refining was waste free, but I wanted to reduce the "house cut" on my refining. I have to agree with Reepicheep, the salvaging is where the mission money is. Just train Trade up a few levels, so you can set the price and wait for a buyer.
So, another quick path might be, get a destroyer, mount some salvagers and tractor beams and buddy up with a fast mission guy to salvage his wrecks for him.
A lot of people like to run missions fast, but don't have the patience for salvaging. Besides, it's more efficient, not to have to go switch ships and warp back.
Just be careful to know the guy first or be in his corp.
I'm planning to work in manufacturing and trade, but you need to buy a lot of training books first to be effective.
The missions are surprisingly repetitive. Mining is less predictable with rat spawns and the odd ore thief (who really doesn't want the ore).