Have you ever wanted for a spell to have a little more "Umph" in strength, honor, or bravery? Have you ever wished for a deity to bear witness to your latest oath to lose weight? Then invoke the gods of the Northmen may be for you!
Now although you seem to know how to invoke a deity into your practice (if not try and find an article about invocation), the gods of the Norse pantheon may prove some issues for those who have never tried working with them before. Here are a few ground rules I've found.
The Norse were very proud people (I mean, boasting is a very honored tradition during sumbles), and the same can be said for their gods. Most will come to find they like being recognized for their deeds, and can even become distraught or just ignore you if you don't. So next time instead of saying "I call upon Thor to-", say "Red Thor, he who wields Mjolnir,the great thunderer, who wrestled with time, who fishes for the mighty serpent, I call to-". Chances are he'll like the second better.
Be willing to sacrifice or offer something for their time. Now I'm not saying to raise a goat for sacrificial purposes (we're Heathens, not barbarians), but be prepared to give something. It can be an action, an item, or even your fealty (in my opinion not recommended). If you can't think of an action they would appreciate in their name, you usually can't go too wrong with food and drink.
Do not put yourself on a low level. Have respect for your deity, but do not grovel in their presence. They will have more endearment towards a man who respects himself and holds himself proudly. UPG from others can say differently (especially in the cases of the Rokkr, but for now let's stay with just the Aesir and Vanir).
Know what you're getting into. If you don't like "larger than life" beings, don't ask for Thor or Odin. Definitely don't call on the Rokkr unless you are committed to drastic and unexplainable change and chaos. Nuff said there.
With these basic guidelines, which can interpreted however you wish, you should be successful. I don't claim that everything I'm saying is fact, I do say a lot of UPG and opinions, it's up to you to judge how much you'll believe. I hope this was entertaining and informative, thank you for reading.
Hail the Aesir! Hail the Vanir! Hail the Rokkr!