Front Attitude Calibration
If you are interacting with plural systems, you should be, at a baseline, expecting different system members to behave differently.
This means calibrating your expectations differently for each headmate, which then requires some effort to figure out or ask who you're talking to.
The most common way to encounter this reality, tends to be with fronts that are ruder or more aggressive than average. While it may be important to respect the boundaries of whoever your system interacts with, sentiments like "I don't like that alter they're scary/mean/rude" or "i miss the other you who was more affectionate" from bad allies, are frequently a result of simply failing to do this calibration.
If you learn what it means when a colder, more standoffish headmate speaks to you - which of their sentiments express genuine affection. If you learn to understand rudeness or playful ribbing as a sign of trust and friendliness. You can map the different expressive ranges within a system to the same sets of things they communicate.
These are even the same skills you should learn meeting new people. If you can, for example, come to understand someone's autistic affect as not simply disinterest and don't abandon those connections.
The cases where plural exuberance oversteps other's boundaries are all very visible failures though. What often fails less visibly are the ways allies failing to calibrate properly can hurt a system.
Many systems have alters who front to handle conflict (either voluntarily or not), but might work to hold their less confident fronts for longer periods and teach them those same skills. Other systems may have less control over their fronts, or even have more fragile and vulnerable headmates triggered by conflict.
What this means is you also need to be able to step down onto a gentler level for interacting with these headmates. Trying to have the kind of heated argument you might expect to function with another adult, with a younger or more emotional part of a system, can easily turn one sided, leaving them feeling distressed or abused. Long term damage to relationships can happen in these spaces, e.g. "i thought they wanted to see me so i fronted, but then they told me off and i shut down and don't really trust them any more".
While it's inevitable to hit some front mismatches, or miss a switch that required a change in behaviour or attitude, these small missteps can usually be easily rectified (honestly just talk it out). What is essential is learning how to adjust your expectations, and not carrying the same expectations onto every system member long term.
This will both make it easier to interact with rougher headmates ("the vriska fictive told me to suck her dick but i know that means she trusts me and feels comfortable around me") and make you safer for the gentler ones ("omg the cute puppy is here again, I'll shelve the heavy discussion for later and get out a plush so they can manage this state better"). Eventually, building your instincts for fronts and moods can allow you to recognise specific alters by these behaviours, or even a more general part of the system. And these skills can transfer, learning to meet singlets where they're at too - plural experiences aren't unique, simply heightened in comparison to the singlet equivalent.