One of the things that I have noticed about my ECA's when they join is that they always want to instantly start making money. They start off trying to put EVERYTHING in their store on their website and basically overload the Market with their stuff.
My suggestion would be to start off by studying what types of things sell most on TC. Once you have gotten a chance to see the "hot" items, start your ECA business to sell some of these "hot" items.