Generally speaking, if there's targeted voting between profiles, a first offense only gets your votes between those profiles invalidated and a warning. If it persists after that, then suspensions are in order.
Another case that usually incurs in suspension — though this one happens at a first offense — is the case of sockpuppet voting fraud. You can read more on that here, and that's usually as specific as we get about it.
With all that being said, and given your last paragraph, I'll end with a bit of the text present in our "targeted votes" mod message template:
The system has processes in place to detect various types of voting between groups of users, so if you know anyone who may be voting for your stuff in kind, please ask them to refrain before the system detects such activity and takes similar actions on their account. If by chance you created separate accounts for the purposes of voting for another, please use the contact form and the appropriate option so you can merge them without further incident.
So, yeah: sometimes the system takes care of things silently, sometimes it provides warnings for mods to take care of it, and sometimes mods may just decide to investigate something if it looks fishy.
So, you ask, what can you do to avoid getting suspended due to this? Mostly, if you just keep to yourself and only have a single profile, you should be fine. In the rare cases when you do keep to yourself but there's still something weird going on, it'll usually be taken care of silently by the system, and you still prolly don't need to worry about it :)