I don't know too many tips in "aikido" like those other than:
1) The energy flowing through your unbendable arm like water through a hose (always pretty good to get started).
2) Think about a fire hose that no one was holding. It spirals around. Imagine energy flowing up your body through your head like that fire hose, and imagine your arms sticking out perpendicular to that verticle flow to be supported by the energetic spirals for techniques from katatetori.
What other ones? Which ones are the most helpful for beginners?
After I do the unbendable arm thing, I try to follow with the unbendable fingers trick.
You loosely put the thumb and we finger together and make sure they form a circle.
Then let someone try to pull them away from each other.
I always tell the students that I image that my fingers are The One Ring from The Lord of the Rings.
Even a little dwarf with a giant axe can not split my ring.
You can see them think: "Silly Dieter still believes in fairy tales!".