I first experienced coaching as an assistant coach to my then 10 year old's FLL team. That overlapped with co-coaching my then 7 year old's Primary Odyssey of the Mind team. I followed that up with being lead coach for the next FLL team.
Every time I've coached I've learned something new. There's so much. Just the logistics can be enough to send me over the edge. Then there's dealing with personalities, both kids and parents. And, of course, you still have to focus on the actual team project.
Luckily both FLL and Odyssey of the mind provide coach support. FLL has the Coaches Handbook, a deceptively slim spiral bound volume that is full of help both relational and technical. Colorado Odyssey of the Mind offers an all day coach training in the fall for the spring season and includes with that a coaching manual in 3 ring binder. Both also offer on-line support and forums.
The best advice I can give is to get involved. Just go for it. Sure, you'll make mistakes, but they're unlikely to be critical, and you'll learn from them. The gift you give the kids is tremendous, but the gifts they'll give you are even greater.