It depends who you want to start as, but whoever you do it isn't hard to quickly start blobbing. Choose the become king of whatever ambitions and do that. Once you're a kingdom subjugate any other entire kingdom that's been formed, so that you're effectively a double king. If you start as the duke of ostatlend (however it is spelled) and upon becoming the king of Norway subjugated Sweden, you should now control 2 holy sites. Work on getting the third in Denmark through either your heir's subjugation of even a fabricated claim. You can also do a conquest of Zeeland if East Francia has a revolt, especially since as norse you should have a huge retinue. Buy only archers for the number and upon declaring the conquest land them and assault. It should tick pretty quickly. You should probably have enough moral authority now, but if your norse brethren have been sucking just do a lot of conquests of slavic/romuvan lands and you should be fine. Help your norse brothers if they get holy warred.