The jetstream is a wide band of high speed wind. Across the Atlantic, it blows from the west and hitting Europe tends to be a little more southerly. Flights to the west try and goaround the less strong northern part of the Atlantic, frequently even as far as the south of Greenland, and even further north if heading to the US west coast or Canada. Eastbound, you want to be in the centre of the jetstream and benefit from tailwinds anything up to 200kts. SO a common route back to Europe is over Land's End or southern Ireland.
You can do a wealth of research on Jetstreams- Google's yer friend.