Income

Credits can be earned from using turns, from selling things on the market, from slave empires, and from artifacts. The most common ways of earning money are turns and the market. As a Terran, you will generally use either Commercial or Agriculture as your main form of income. Commercial provides a stable income that you can see immediately, while with Agriculture you will usually have a negative credit income and make your money by selling food. For beginning, I`d reccomend Commercial. Research Commercial Infrastructure, to level 20, then research ships and clusters from the Research Tree. After you`ve done this, you will want to get more planets. That can be done by either exploring or attacking. Make sure to build just enough housing on your planets to get a population equal to or within 10 above the total land of the planet, and assign all the rest of the land to Commercial.

for a terran the most reliable income is from comercial.
To set up your home planet you must first ensure all the ore is removed from gthe planet by using turns on researching comercial until it is al gone.
Then ensure you have 50 housing infrastructure built on your home planet so you have at least as many people as you have land.
Then remove all the infrastructure from mining and agriculture, and assign all the free land to comercial.

This gives you a nice stable base to build an empire on.
You buy all food and minerals from the market using your cash, and put all infrastructure research into comercial. you do NOT need to buy consumer goods.

i plunder.. :)

Depends on what race you are. Infrastructure research will increase the effectiveness of each infrastructure you build on a planet. There is no "best" income for any race, though there are "strongly suggested" incomes and very difficult to use incomes (like tax terran, not easy but works) and horrible incomes (like plunder terran, just won`t work...)