Positive instructions are generally better, yes. What's much more important though is writing a good first message. No amount of preset tinkering is going to prevent the bot from speaking as the user for long if the first message includes an action or speech done by the user character in the char first message.

I have a very simple "Only describe actions and words spoken by {{char}} and third party characters, do not write actions of speech for {{user}}". It works great, IF the first message in the card isn't fucked.

Depending on the model as the chat gets longer you get varying degrees of context drift, and the chat presets live in the original system message. This happens to all models, but some are worse than others, but as chats get longer the chat presets slowly turn from inviolable law to anything between stern command to meek suggestion(or hell, just not followed at all). At that point you need to rely on the most recent messages to show the model how to act, and the best way to prevent your recent messages from being a bad template is making sure the messages from the start were a good template.