I use a mix of EEstats market history and the in-game market news to price my goods, but I still get tech stuck sometimes. Then depending on whether I need my goods sold in 12 hours or 18 hours, I price them according to the average prices. If I need them sold off quicker, price at or a little below average*. If I am going for my 18 hour bonus, I usually price a little above average*.

Another thing to watch for is changes in volumes sold each day. If suddenly more of one good is demanded and the market becomes empty of it, prices will usually rise to meet the increased demand. On the other hand, if demand suddenly falls and goods get stuck, prices will usually decrease in an effort to sell more.

*This is considering that prices are fairly stable and not crashing or rising by the $100's each day..