It is impossible to list all skills that would be suitable to generate fiat / BTC earnings. There's demand for thousands of different things. Maybe I misunderstood your concern, but I don't think that it is very Bitcoin-specific.
Just browse the marketplace section of this forum to get an impression and some ideas of what's on offer (and marketable) in the Bitcoin sphere. However you can still offer anything (legal) you want. Think about your skills and if they might be helpful to other people. If you are not sure, just try - you have nothing to loose by making an offer...
trading is the most effective way to earn btc and become a billioner. you need to have full knowledge about the market, a positive mind and ofcourse some luck. you can also start mining
What a horrible advice! :/ Trading will most likely generate a highly negative return - unless you have a lot of luck of course...

Mining nowadays is only profitable for big, professional operations with significant investment capital and favorable electricity rates.
ya.ya.yo!