I'll throw in my 0.02 ..
Open carry is different things to different people, and IMO that is what can potentially create issues with the public.
In my opinion, what I call "real" open carry is quite boring. It is simply going about one's daily business as usual, and being visibly armed while doing so. It also (hopefully) involves decent situational awareness, so that one is aware of potential threats.
In many cases, open carry is something many people are not often exposed to (at least in some areas), and because of that, it may involve having discussions with people (store employees, curious bystanders, police officers) about your firearm. It may also involve having to decide whether or not one is willing to patronize a business if open carry is not welcome at that business.
If one wants to promote normalization of open carry, then one MUST be civil and polite during these discussions. If they are, then they give a good impression of gun owners. If they are not, they give a very bad impression.
In theory, open carry is basically the same as concealed carry, other than that one's clothing covers up the firearm in one case, and doesn't in the other case.
However, some people have the impression that open carry is not an ordinary activity, but instead is a form of political activism. This impression is bolstered by OCers who make a show of the fact that they are open carrying a weapon, and is firmly reenforced by those who have aggressive and/or confrontational discussions with either law enforcement, store owners, or other members of the public.
This includes what was happening (in some cases) at Starbucks. Some people were not, in my opinion, simply engaged in open carry - they were engaged in political activism, as they were gathering in a group for the explicit purpose of showcasing open carry.
Now admittedly, some people think that ANY carrying of a weapon is a political show, even if one is not doing anything other than going about their normal business. Those folks would be wrong ... but that's not going to stop them from thinking that way. We may not be able to change their opinion, regardless of how polite and well-behaved we are ... and that's simply the way it is. It's the others who may be on the fence that we have the chance to convince that open carry is not a bad thing (and actually a good thing).
In my opinion, the best policy for an open carrier to follow is to always be polite and respectful to everyone - even if they are not polite and respectful to you. Respect the rights of store owners to exclude you from their property if they desire to (as that is absolutely their right to do so). Just "be nice" in general. I think that that gives a much better impression to the world of open carriers than that which is presented by in-your-face activists.
And if one is going to engage in political activism, it should NOT be at any business that wants nothing to do with political activism (e.g. Starbucks, which had previously expressed a NEUTRAL position, not a pro-gun position). It is not sensible for us to demand that other people respect our right to open carry if we do not respect their right to control their own property.
Even businesses that support open carry don't necessarily want a dozen open carriers converging on their store and possibly making a scene. There are exceptions, of course (e.g. I'd guess that All Around Pizza in Virginia Beach is fine with that) but most businesses want to sell to as many folks as possible, and don't want some of their customers to be intimidated by others.
Some other quick thoughts ... as far as I'm concerned, unless you're in an area where the chance of a wild animal attack is a fair bit more than "very slim," I'm not convinced that OCing a rifle is a good idea. I also think that if one is out in public OCing, one should never unholster a weapon unless it is absolutely necessary for self-defense.
I think it really boils down to "be polite to everyone and be respectful of others." When we are rude and disrespectful, that hurts the open carry movement and gives us a bad reputation. It doesn't mean you're going to convince everyone (or anyone) by being polite and respectful, but hopefully at worst, you'll give the impression that OCers are polite people.