I make a few hundred dollars a month selling stuff on ebay, and usually put in about one afternoon's worth of work taking photos and writing item descriptions. I am hardly a high-power, high-grossing seller, but I've made money with very little effort. Here are my tips:
1. Take good photos (same as Craigslist, but ebay buyers expect more photos). You can add up to 11 photos before you have to pay, and people want to see the item. Upload close-up photos that both highlight the item's attributes and disclose any flaws. Which leads me to...
2. Be conservatively honest in your item description, but don't hold back from selling used items. People are surprisingly forgiving of less-than-perfect items when you are honest with your listing description and asking a fair price. I've sold clothes that had small stains, obvious wear-and-tear, and other "flaws." FWIW I have a 100% positive feedback rating, so none of these things were a problem for the buyer. Sometimes people are looking for an item for a sentimental reason or to repurpose into something else, so don't exclude items that might not even serve their original purpose well (e.g. almost threadbare sweaters).
3. For most items, shorter auctions with a "Buy It Now" option have resulted in the best outcomes for me. The default search results ranking is by items ending soonest listed first. I almost never have a bid on my items until the last 2 days. I typically use the 3 or 5 day auction option, and I don't really see the point of the 7 day auction, especially since relisting is automatic and currently free. The one possible exception I've noticed is rare collectible or artistic pieces, where buyers are more likely using super-specific search terms and there are fewer other options already on ebay.
4. Pay attention to shipping cost. Ebay does a pretty good job of estimating the cost of different types of shipping, but you have to make sure to input accurate information when you are on the shipping options page. For example, it often assumes all clothing can be shipped in a packet/large envelope, which is often not the case with sweaters, blazers, shoes, or other bulkier items. Make sure you either put in an item weight or package type that will give you and your buyer an accurate estimate for shipping. I sometimes take a small loss on the shipping cost, but build that into my item price.
5. Look for sales on fees. Most of the things I sell go for ~$30. I am not turning a huge profit and I'd like to keep as much of it as I can. Ebay doesn't charge any insertion fees for standard listings until an item sells, but once you start selling, the fees can add up. You can save drafts of your listings and even upload the photos, then wait for promotions where they reduce the the fees for items inserted during the promotion by half or more. Sometimes they also do options to add extra features to your listing, free of charge.
Good luck!