Okay for Thieving start off by typing ::thieve
Now your at Edgevile with a bunch of stalls.. start off Thieving from the "general store" stall which gives you 50k per steal..i recommend doing this method until 60 Thieving.
Now that you have 60...Start Thieving from the gem stall..this will give you 550k per steal..do this until 85 Thieving.
Now that you have 85...Start Thieving from the "Silver" stall..this will give you 900k per steal..do this until 99 Thieving.
Now that you have 99, you can start Thieving from the "Silk" stall, this gives you 4m per steal..and a hefty amount of experience along with it.
Good luck getting 99 Thieving!
Oooo, cool little fact..they misspelled Thieving in the skill tab.. =P