Posted this somewhere before...
Just work your way up from small stuff. Sell everything you have now, and search for players for the amount you have and under. Go for mainly the auctions starting at 150, they'll go for lower than usual most likely. When you've been using it a few days you'll generally know what most stuff is worth so you'll be able to see what you can make profit on. When you have 7.5k to blow, I recommend when you have about 10k, buy a gold pack and hope you get something good. If not, work your way back up to that figure again...
Thats what I did, I got a bit of luck and got a Nilmar in a pack, sold for 17k, and since then I've been buying Pedro's for around 12-14k and selling for 16-18k. The more you have, the more profit you can make on things...