I realized this is probably a common thought.
I can only share with you what I know works, so here is some anecdata for you to enjoy:
When I started out, it was simple enough to BUY things on the sales comm. But selling? No. I purchased a dress out of an older Metamorphose Lucky Pack and when I decided I no longer wanted it, I asked my friends list first! (I cannot express the importance of making friends in this community, advice-wise, style-wise, and so you can help each other when it's needed.)
Apparently the dress I was selling was EXACTLY what a friend of a friend was looking for. That was my first positive feedback.
There's also a very great guide by nessaneko in the memories: http://community.livejournal.com/egl/10180939.html
You can also get good feedback from being an excellent buyer in the comm. There are plenty of ways to get started, so if anyone has any advice/anecdata, I would love to have it compiled here for current and future lolitas.