Approaching a potential partner is essentially the same, whether you're poly or mono. Dating is pretty much the same for any given approach to relationships.
You are likely to give bad vibes by disclosing other relationships early on whether you're mono and dating more than one person or actively poly. Were you mono and said you were dating other people prior to her deciding she's interested enough to date you, then you might scare her off. Same applies with being poly.
Disclosure also happens with the same sort of schedule. When it's time to discuss the possibility of dating "seriously"--which in mono circles would involve exclusivity--is when these things get negotiated. Sure, some places have the odd approach that if you've dated somebody twice, you're assumed to be exclusive; I find those places actually uncommon, at least here in the US.
When speaking of various forms of non-monogamy...it ain't poly if you're just fucking around.
While polyamory, open relationships, and swinging are all distinctly different approaches to non-monogamy, they are not mutually exlusive. Folks can, and some do, engage in more than one of them at a time--and it's all good.