I'm gearing up for my yearly ebay selling session. We usually sell things from September to November - although the holiday season is so hit and miss with non-paying bidders to contend with. However, we have always come out ahead in the end. We've been on ebay for nearly 10 years and there are ups and downs - I don't think I like it as much as I used to (I feel like they have really squeezed the small-time sellers like me out), but it is still somewhat profitable so I'll keep at it.
I like to list clothing in big lots - don't take the time and energy to list items separately unless they are really high-end/brand new. For almost all of the clothing we have ever sold, I take a lot of pictures and describe things the best I can - then start the auction at 99 cents and let it go. I've never been disappointed - I have always made more than I would have at a yard sale. Kids shoes (in excellent condition) are another category where I have done very well - be sure to clean them up before you take pictures.
My philosophy is nearly always to start auctions at 99 cents with no reserve. It is the cheapest way to list and a better way to attract more bidders. The only down side is that you might end up selling your item for 99 cents, so make sure you're OK with that ahead of time.
Shipping - man is it expensive to ship stuff! If you can use Priority flat rate boxes, those will simplify your life immensely - but I'd reserve them for heavy items. Priority mail is based on weight AND size now, so the smaller the box, the better. We try to use bubble mailers when feasible as well. We get free Priority boxes from the post office, recycle other boxes we receive or find, and use plastic bags from the grocery store and newpapers as packing materials. I try to weigh everything before I list it to get an idea of how much shipping will be and I always try to charge actual costs. Incredibly, my "shipping cost" score is good, but not perfect, even though I have lost money on shipping more than once. It is OK to build in a "handling" cost (maybe $1 or so) to help cover your shipping materials, but people will detect if you are trying to pull one over with inflated shipping fees (like the person who wanted to charge me $30 to ship a toner cartridge - no thanks!) - not to mention that it is against ebay policies.
Sometimes I will put a Buy it Now price on an item of about $5-10 more than I think it will sell for and offer free shipping. That way, shipping isn't really "free", but the buyer perceives it as such. Does that make sense?
We also list seasonally - I'm getting Halloween costumes ready to go now. They must multiply in the closet because I swear we sell several every year but always have several more to sell the following year.

Anything holiday related won't get listed until the first of November. Any toys or kids items might do better in November as well, as people start looking for holiday gifts.
Is it worth it? Well, for me, yes - I sell stuff we have laying around the house anyway (man, we have a lot of junk!), sometimes DD's clothes she has outgrown - anything I'm not using. I don't have a lot invested in the things I sell - we have used them or acquired them so long ago that their value is diminished to us, so whatever I get, I'm happy with. If you go in expecting to make a small fortune, you may be disappointed. If you hope to make a few bucks off of something that was just taking up space in your home, you may be pleasantly surprised.
Good luck!