One good way- if artiface or armstace, buy the schematic for the temp power needed to fight nightmare pilgrim. Costs like 20 daily comms. Then just Goto belsavis in the daily area and pick up the nodes. Perfect uptari crystals are what u need if artiface. Then just craft the temp power. Its called gormack power crystal. They sell for 50k on the gtn. Easy and quick to make. I sold 5 yesterday for like an hours work. Also, do the dailies, you can earn 100k just from doing the dailies.
To get more SWTOR credits, you need to collect items in lower price. Then you can sell them at a higher price and get more credit. Complete the missions and quests as this allows you to get rewards like armor and weapons. Visit http://www.swtorpwnage.com/how-to-make-credits-in-swtor for more details.