How to avoid plagiarism?

Hi!

I'm new to the warrior forum, I often heard about it, now looked at it myself and apparantly its the biggest forum for internet marketers, that's why I think at least you are able to answer my question

The problem is I dont want to get into trouble due to plagiarism. What is legal to copy and what isn't?
and more importantly:

what is accepted by the competitors?
(I don't want to get a bad reputation, since I want to do some JV's with them, and actually, I like them since I learned from them, too so I have no intention to hurt their business)

I mean, knowledge doesn't miracously fall into somebody's lap, everybody learned from somebody or somewhere.
So may I use what I learned in a seminar to sell my own products?
May I use what I researched in the internet?
May I use what I learned from other products, like ebooks videos etc?

Of course, I don't just copy directly what I want to "use". I want to combine the little "truths" from various knowledge sources and want to create a "new" product that describes the topic and solves the customers problems in my personal, own way, all the information would be conveyed through my personal perspective.
It's not my intention to "copy&paste" my competitors texts to save work. I DO put effort into it, i'll do it differently in my own way, still, my question is may I do that, even if a lot of my knowledge comes from competitors products?
(well the most knowledge comes from free sources, but my best ideas are based upen my competitors ideas which I processed further)
I also found out a lot by myself by combining different sources, discarding the mistakes and only taking the best from each source, I could make even a more high quality product than my competitors...
Is it wrong to do that? I mean, nobody has to tell me that all my competitors (doesn't even matter in which niche) invented everything themselves...

What is accepted to "re-use" from others and what is sooo unique that it's not?
If an idea is that unique, may I at least take it with reference to the competitor and comment on it/elaborate on it? (cause the elaboration was my "intellectual work" the problem is, I have to present my competitors idea, so I can show how I elaborated on it)
what if that idea is contained in a charged product? May I elaborate on it even if I risk to reveal fee-required information from my competitor to my customers?

I'm not asking how to get away with plagiarism, I'm asking how can I build upon other peoples ideas without pissing them off?
Do you have any strategies on that? I think most of you have to deal with this, since, no matter how unique your product is, as long as you have competitors you must have something that is similiar, else you wouldn't identify each other as "competitors"

So what are your thoughts on this?

I 'd gladly give a concrete example if necessary.