If instead of saying what you would do, or what you think they should do, you express a concern about the code, the tone is completely different. Now it's just saying something like "do you think repeating this across files will be problematic?", which allows the other person to be the determiner. If they agree they may well do exactly what you would have suggested, and if they don't, it can start a discussion that helps bridge together how various team members code. It's win/win.
It also helps people understand what you aim for when writing code, which helps them keep in mind your needs in the future (and vice-versa for you to keep in mind their needs).