Vikings are pretty simple early on in the game, one province produces troops the other ships so you can encircle the british isles (which doesnt take very long then you can have it pump out troops)
Just sail up and down the coast and rock and roll and raid everything burn it and run dont stay to long.
Then once you get a lot of florins, about 20,000 or more start holding on to provinces and building and raising the big armies.
Or some variation on this tactic but its rather simple compared to the other vactions in the viking campaign.

Another note, get some assasins early and take out priests if possible. I was always freaked that I would lose my raiding privelages.