Play up all of the advantages of independence (even imaginary ones), and downplay all of the potential costs, promising that a change in who is sovereign is really not so consequential except for when it is.In the Quebec case, in past campaigns, folks were told that they could still use Canadian passports and other such conveniences that come with Canadian citizenship even if one is no longer a citizen.
In the Scottish case, the hope of the Scottish National Party was that they could promise independence from the United Kingdom (or Great Britain, I am easily confused--must re-watch this video) yet get slid back into NATO on a fast track. Alas, the SNP's past stances on nuclear weapons--that the newly independent Scotland might be a nuclear weapons-free zone--runs up against an old NATO nightmare--the painful deployment of Pershing missiles to Europe in the early 1980s. Because Scotland has been home to a nuclear sub base, and the SNP wants to close it, NATO has said that this would be a problem.
Now, the SNP has to figure out how to finesse the party's position with NATO's stance and yet still promise that independence will change nothing in Scotland except for all of the cool stuff. I have no doubt that the SNP can find a way to gloss over this. After all, if Quebec can promise referendum voters that they can keep all of the cool Canadian stuff, like passports, but not pay taxes or have any governance emanate from Ottawa, I am sure that the SNP can spin this as well.
Oh wait, Quebec failed twice to gain enough votes (merely 50% plus one), so perhaps democratic publics might just understand that dramatic political change may have some costs attached.