There are various jobs and duties within the UEC that earn credits quickly.

For players that wish to earn credits solo here are the secrets:

-Trading ships cargo inventory can be more profitable than most other professions, ideally a large Hercules or Caterpillar or Carrack will suffice
-The most profitable asteroid to mine is Quantanium Fuel which explodes 15 minutes after being first collected in a cargo bay, ideally a prospector, or a mole, or an Odyssea would do just fine
-Being a Bounty Hunter or Tracker can earn you 300k UEC an hour with minimal risk to losing all your efforts unexpectedly

Then there are Duty Crews… …Our Duty Crews or members of all 6 groups can earn profits even faster as a team. Our teams are treated equitably and instead of earning a set amount of credits per hour, we earn shares of the final sales. Every member is entitled to a share of the profits for their share of the work. 

Some minor notes to be clear about:

-The shares are all equally divided 1 share per person (to be paid 1st)

-The Project leader (if it applies) gets an additional 1 share (to be paid 2nd)
-The Quartermaster (if it applies) gets an additional 1 share (to be paid 3rd)
-The Accountant (if it applies) gets an additional 1 share (to be paid 4th)

-The Criteria 6 Political Organization gets 3 shares to distribute between 6 groups (to be paid 5th)

-The Organization group gets 1/2 share
-The Corporation group gets 1/2 share
-The PMC group gets 1/2 share
-The Syndicate group gets 1/2 share
-The Club group gets 1/2 share
-The Religious group gets 1/2 share

-The Owner of the vessel gets an additional 2 shares (to be paid 6th)

-The Captain of the vessel gets an additional 2 shares (to be paid last)

-The Captain is responsible for reporting accurate profits earned and temporarily holding the various 6 group shares until leadership arrives.

-In the event that the vessel is not making enough profit, the Captain, the vessel Owner, the Project Leader, and the various 6 groups will not be paid and the remaining funds will be equally divided throughout the rest of the crew.

At the moment the minimum amount of profit required for a Captain or Project Leader to earn profits is 30,000 UEC per hour. A good Captain and Project Leader will know how to earn between 60,000 and 300,000 UEC per hour for every player. Captains that fail to earn at least this amount for their crew can be subject to being replaced by more effective Captains. 

If the Captain or project leader cannot earn 60,000 per persons share per hour, the crew may promote the quartermaster at any time.
If the Captain or project leader cannot earn 30,000 per persons share per hour, the company will transfer that captain to a more suitable roll