Just checked your profile. Age 18 the world is your oyster.
The big money earners are nuclear and oil & gas, lot of new build nukes coming up in the U.K and there are a several new oil/gas fields opening up overseas, Baku, Angola and NW Oz . More money in oil but you will need to travel and can be difficult to break in to. Nuclear, you will need security clearance and some experience in your field
Another field to look at is private super yachts, but you will need your marine tickets, and the economy is obviously suffering a bit, but the rich still have their toys and they still need fixing. Good money and often tax free with lots of perks i.e your wages are pocket money, as food and accommodation are all sorted for you.
You might want to try contract work to get your foot in the door, be warned though it gets addictive, I started 20+years ago as a temporary thing!!!!!!
There are lot of broke, divorced, alcoholic contractors out there.
Welders can earn more than engineers if you're prepared to work hard and smart (hard alone just gets you burnt out).
Good luck whatever your path, it can certainly be a wandering one.
I started as a marine engineer playing around on small boats and yachts, I currently work on a nuclear power station, played with genetic research machines, built satellites and worked for the sub-sea oil crowd along the way, who knows where I'll be next???
There is a desperate lack of new blood with hands on experience in engineering these days, every outage on power stations is getting harder to find people to do the work. i.e someone I know had 72 men booked in for inductions, 9 turned up!!!!!