Andy has it right, but even with proper technique a front derailleur setup that's a bit off can be fine until you hit the road. The other question is what guidance did you use for the derailleur setup? "Fiddling" with it does not tell us whether you used a good source (sheldonbrown.com, parktool.com) to set up the derailleur height and angle, which are necessary before you start working with the limit screws or cable tension. Throwing the chain off is very common with a too-high derailleur position, as the limit usually has to be set further out.