Can't really add any tips here as everybody has covered everything I can think of. got a couple of stories though. First one was a few years ago this guy at our club was running up his engine. Saito150, and had shown a tendency to throw props(improper starting and adj. habits). this guy had been warned before and had had a couple close calls, but here he was, sitting in front of that engine and running it up to full throttle. Suddenly we heard a loud "pop" and looked over to find the guy lying on the ground. the engine had thrown (again) and shattered the entire prop/spinner assembly. Part of the prop hit him in the inner thigh about six inches below his "bit and pieces" and left a deep cut that needed nine stiches. Worse still was the biggest part of the spinner that was left hit him in the chest hard enough to bruise his sternum and cause heart palpitations. He was in his mid thirties, previously healthy and was out of work for two weeks after that.(We worked for the same company) Had he had a heart condition, he may very well have died.
My other story is about me. Saito 1.50 again.(not the same one!) Was breaking it in in my yard, had reached the "full throttle lean it a bit" stage. Had been running for about a minute since my last adjustment. it was at WOT and sounding good. walked around front of it, watching and listening to it run, POP! backfire, didn't toss prop but did shatter spinner. could feel the displaced air on my ear as a large chunk of it whizzed past.
The only thing i can say is there is NEVER A REASON TO BE IN FRONT OF A PROP/ENGINE THAT IS RUNNING ABOVE IDLE!!!!!!!
Can't count he number of time I've seen props spun but not thrown. someone got lucky every time.