Been playing for almost 2 months now. I have made well over 10 million credits. My highest level character is 30.
HOW!!???!?!? I am sure you are asking...
Crafting! Yea, crafting... Most people hate it...but what craft you say??? That really depends on your server. Things are always changing as well. One month mods sell for stupidly high prices, then the next month they crash due to over flooding of the market, because everyone in general chat says make mods to be rich lolz... This is where being smart enough to stay ahead of the market is going to pay off. Also, having alts. Become a Master Crafter (450 skill in EVERYTHING). Yes, this can take some time. I myself am not completely there. I do have everything in the 350-450 range though, which is working for me right now. One week I will do just harvesting of crafting mats, cause everyone else is crafting items, so that market spikes. Next week harvestables crash, I then buy out the cheap stock, and craft items instead. Again, depending on your server, this can change faster, or slower.
You can also get away with just harvesting, mainly picking up Slicing, sending your side crew members for lock boxes, at some grades tech parts, for the change at schematics is worth a lot more... Bioanalysis, Scavenging, Underworld Trade (only for metals). Those also work well, but those can fluctuate in market prices. Slicing lock boxes will always get you credits back (sometimes crit a schematic, low grades tend to sell higher then the high grades), more at higher skill. I have yet to see Archaeology turn much of a profit on its own.
This part is shady...but it works...a lot... Most the time you will get the mentally retarded, who some how have stumbled across the GTN. They place items up for sale for stupidly low amounts, then get undercut by 1 more moron. If this is an item you KNOW sells for a much higher price, and quickly, buy them out, and re-post at a higher amount!!! I have flipped so much profit in this game it is how I make a lot of it, even more so on weekends!
Hope some of this helps, this is what I have been doing in MMOs for 13 years now.
I am that low level twink you will come across, who has no high level main