When it comes to being casual, using informal language can be a great way to convey a sense of ease and relatability. There are several ways to say that you want to be informal, such as saying that you want to keep things laid-back, easygoing, or unpretentious. You may also hear people use phrases like "let's keep it low-key" or "let's not be too serious." If you're looking for even more synonyms, consider using words like relaxed, informal, or casual. All of these phrases have a similar meaning and can help you to convey a sense of familiarity and approachability in your conversations.