I started keeping cichlids in the 1950s, and have made thousands of mistakes.
I have killed many, many fish, as will everyone who keeps them.
My replies to threads are things I have learned "because" of those mistakes.
But I also know fish keepers who can do things that would kill a beginners fish, because they have experience. These keepers can cram small tanks, or a small pond, and/or put fish together that normally won't work.
Although they can, most people without experience, probably can't.
I agree with dogofwar, talking with experienced keepers in fish clubs and becoming educated will go a very long way. Although this is a hobby, its not like collecting stamps, if there is a screwup, stamps don't die.
The advice experienced keepers give, may not be what you want to hear.
Just because you want something, is not always a great reason to get it.
Proper stocking is one of the "the" most important factors to success.
Less is more, and learning what will live together, and what will create a bloodbath before it happens goes a long way to saving grief and hard earned cash.
I am always amazed by posts that say, "I want an aggressive community" and then the same poster is not surprised by result and posts a followup "why are all but one of my fish dead"?
Or "I want a dovii, or umbi but I only have a 55 right now. Of course I will upgrade soon".
Sorry if I sound cynical.