Be very careful about accepting player courier contracts. Some are scams that are impossible to complete (they set the destination in a player station that neutrals don't have docking rights for), or are located in such a risky set of space that they expect you to fail.
Trading is also a very viable career choice, but it needs a fair amount of investment and much like Bacchanalian's comments on PVP, there is no chance of you being able to compete with well established manufacturers (at least initially) since their overheads are much smaller than yours through both skills and well researched blueprints.