Angelfish Help

I've never had much luck with Angelfish in my small 10 gallon tanks. 
I've just purchased a new 30 gallon tank.

What are the "secrets" to healthy Angelfish?  What types of other fish
are appropriate in a tank with Angelfish?  Are there any specific
conditions that are conducive to health Angelfish or things I need to
avoid?

Thanks
Fred
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