There are multiple ways of going about this. The one that most people recommend (especially for newbies) is to keep the worship of each pantheon separate, give them their own spaces and honour them the way they are honoured in their native cultures.

However, some people also practice syncretic traditions (that is, a blending of two or more religious traditions, like if you, say, practiced a Hellenistic (distinct from Hellenic) tradition, or adopt deities and traditions from cultures that had a lot of contact (I do not do this myself, but many Vanatruar are interested in Celtic–particularly Irish–traditions because of the similarities between them) with each other.

Research is very important here. If one deity is traditionally offered pork while the other absolutely despises it, it’s important to find that information beforehand before you get in trouble by offering them both bacon. Read up on all the cultures involved. Do they have particular requirements re: ritual purity? Are there any special rules for a particular deity’s cult? (ie. No weapons on Freyr’s altar. No removing Nerthus’ veil, etc.) It’s important to get ground rules established and to figure out how you’re going to negotiate relationships with so many deities and spirits.