eBay relies on trust, but this is backed up by a feedback system. People who have traded with one another can rate each other's behaviour, and their score is shown next to their name - click this number to get a breakdown of their feedback.
The longer you've been with the site and the more good feedback you have, the more confidence buyers will have in you. As you haven't sold anything before, it's worth building up your feedback score by selling some smaller items before you try and sell anything of high value.
eBay charges insertion fees based on the reserve and final price (called the Final Value Fee), while PayPal has a small fee too.
Roughly speaking, if your item sells for £10, you'll get around £8.70, if it goes for £50 you'll get around £44.60. CDs and DVDs have a lower insertion fee and a higher commission, which will leave you better off unless it's a very high value collector's item.
There are two things to do before you start:
1) Work out the postage and packing cost
If you're not sure what this should be, you can always quote the average price other sellers use for similar items.
Considering offering shipping abroad: if you're selling light stuff like DVDs, jewellery, books, clothes, etc, you will get around 25% more bids - and therefore more money - if you do.
2) Take a photo
Take a good, clear photo of your item; preferably against a neutral background (a bed sheet is ideal). If there's any damage or details you want to highlight, take some close-ups.
Even if it is a standard item in new condition, a photo of the actual one you're selling inspires confidence and will help increase your price.
eBay recommend that images are between 1000 and 1600 pixels on their longest side. Transfer the image(s) to your computer and save them on your desktop.
Now you're ready to list your item.