Stand the bottle upright for several hours before decanting. This will help the sediment in the wine to settle a little and will make the decanting of the Port easier.
Before you start, have a clean decanter at the ready. Alternatively, you could also use a clean empty bottle or a jug. Without shaking the bottle too much, remove the cork seal around the neck of the bottle, wipe off any dust that may have accrued and carefully insert the corkscrew. Depending on the age of the Vintage, the cork may have been in the bottle for many years, so it is important to treat it with care and pull gently from the bottle, so as not to snap the cork.
Slowly pour the Port into the decanter. A funnel can be useful at this point, although not entirely necessary, and particularly with older bottles of Vintage Port which will naturally have more sediment, a small piece of muslin cloth can help to catch any deposit from entering your decanter.