Start off selling small, lower priced items to build up your feedback. Once you become somewhat repuatable, with maybe 20 feedback, then sell any higher priced items, as people will trust you more, and likely bid more.
Make sure you do everything you can too make the customer happy. Ship the item as soon as possable, i try to get stuff out either the same day, or the next day after they pay.
List the item exactly how it is. Do not hide anything. If your selling a cell phone because the call button doesn't work, make sure you say that.
Insure high priced items with delivery conformation.
You get more for items when they end on sunday, its been proven.
Save yourself money by starting items off at a lower price. If i expect to get $300 off a video card, i will start it at $9.99.
This attracts more bidders, trust me it will sell for the same amount as if you started it at $199.99, and quite possably even more, and you will also save on fees.
Only use reserves if you really feel it is necessary..as they tend to detour bidders.
Do not argue with the buyer. Do not risk negative feedback. Communicate, let the buyer know when you ship the item, give them the tracking #, and thank them for there payment.
On higher priced items, (about $300+), i tend to deny bids from people with 0 feedback. Alot of times they are unregistered, scammers. I have had my auctions screwed over too many times be these bidders.