The first step is to choose an auction site, the best known and most popular is www.eBay.co.uk. It’s used for selling all manner of items from cotton reels to cars. Before you list your items for sale have a browse and find out guide prices from other sellers for similar items. Other auction sites include QXL and eBid, which offers free auctions, setting it aside from most other auction sites.

An alternative to auction sites is  Amazon Marketplace. This is similar to a shop and allows you to list your second hand items next to the new items Amazon sells.

This article will focus on eBay.
If you have not used eBay before, you will need to register a name for which you’ll need a credit or debit card.

To list your item click the Sell link on the eBay homepage. You will need to understand the listing format either auction-style or a fixed price sale. Then you need to select a category where the item will appear and you can enter key words so that various searches will find your item. Next, enter a title and description for your item. Do this with as much detail as possible to eliminate confusion or misrepresentation.

It is beneficial to upload pictures, they are almost essential to the sale of your item in most cases. Take shots from all angles and include any damage, wear and tear or missing parts. Buyers need to have all information both within the pictures and in the description of the item. Beware, the more pictures you include, the higher the cost of listing the item.

Nearly there - set a reserve or buy it now price and complete postage details and costs. Consider the cost of packaging when setting a cost. 

Fragile items will obviously have to be carefully packaged. There is a cost associated with selling on eBay so ensure this is covered.

Now choose your listing duration. Most auction style sites last seven days to attract the maximum number of buyers and give them enough time to research and decide.

Before you commit to the listing it can be previewed.

Positive feedback is essential to become a successful seller. In order to achieve this you will need to describe your item fully and accurately, answer emailed questions promptly and politely and provide adequate postage options.

Once the auction closes and you have a successful bidder at or above your reserve price, contact them and make arrangements to accept their payment. When the money has been received and,
if paid by cheque, when it has cleared, pack and ship the item to your buyer. Unless you stated otherwise, you must do this promptly. Pack the item carefully so it travels safely; you should insure the package if the purchaser requests and it’s a good idea to insist on insurance for breakable items.

So no need to live amongst clutter - get selling online.