The Vikings tended to both farm or fish or follow a trade and go on Viking raiding expeditions.

The Vikings followed seasonal raiding patterns.

The Orkneyinga Saga, describes how in the 12th century (late in the Viking Age), Sveinn Ásleifarson would supervise the planting of his lands in Gáreksey in the Orkney Islands, then take ship and go raiding. He would return for the harvest, then go raiding again and return around Yule.

Sveinn and his eighty men would spend the winter in his great drinking hall, the largest in Gáreksey.

Sources: http://www.hurstwic.org/history/articles/society/text/raids.htm http://books.google.com/books?id=P1gAAAAAYAAJ&pg=PA139&lpg=PA139&dq=gareksey&source=bl&ots=PPKHwSDDYr&sig=x5Deq_xP-KtQ6zE-npXpTsOX1_c&hl=en&sa=X&ei=vDS_UtnfA4TisATJs4CYDQ&ved=0CEgQ6AEwBg#v=onepage&q=gareksey&f=false

This seasonal raiding pattern was common, though, in the height of the Viking era in the 10th and 11th centuries, large raiding groups might fortify winter quarters so they could overwinter in their target locations and not need to travel back and forth from their Scandinavian bases.

The Vikings, of course, gave no notice to their targeted victims. They preferred to strike by surprise from the sea, gather loot and treasure, and be back on their ships before resistance could mobilize. If in larger numbers, they might well threaten their target, and negotiate a payment to refrain from raiding. That way they could get loot with little effort.

How much loot the typical Viking earned is not well recorded. Luck probably played a great part and success varied from fabulous wealth to busted voyages where the (surviving) Vikings barely made it home with food and supplies exhausted.