It really depends on what you want to sell, and what you think will make the most money.
I would reccommend starting out with something small like accessories.
Whilst the profit margins are originally small, so is the financial investment. If worst comes to worst, you might only lose a couple of hundred bucks.
Probably one of the most important lessons to learn, is not to be greedy. Even if your profit margins are small, it is still profit.
As you get more experience in the game, you will begin to spot trends.
Hope this helps.