Some people make money with cards - but mostly what I learned is to only collect stuff I want for fun and buy it with no intention of selling anything (I have over 500 signed BYU/LDS cards, and probably 100 signed hats, helmets, mini-helmets, 8x10's, flooring, footballs, basketballs, soccer balls, volleyballs, etc). I just wish I'd run across someone who wants to buy all the cards that I have that I no longer care about.
I have a few cards listed on Ebay - but if a card is selling for around $40 when I check actual selling prices, if I list mine for a starting price of $5, somehow I end up selling it for $5, but if I list it for $35 nobody bids on it. I guess I just don't do it right, so don't take selling advice from me. 🙂 I suspect when I get around to selling my 50's and 60's cards, I'll try it on Collx.