You need to have slicing at 340+ and a speeder then go to Ilum. Stats from my last run with a level 25 non-stealth char:
Time: 18mins
Died 1-2 times
5 chests = 22k
15 slicing lockboxes = 24k
greens vendored = 4k
1 mission discovery
Chests respawn time is about 30min so you can repeat it soon after to get 100k/hour, probably fastest way to get credits at lvl 25, with the right path you can avoid almost all the mobs. The route works for empire side but for republic side you could figure out something similar. Best to do it at quiet hours, doing this at lvl 25 can get you banned..