When it comes to expressing the act of remembering something important, "keep in mind" is a commonly used phrase. However, there are other synonyms that can be used to convey the same idea. For example, "bear in mind" has the same meaning, but with a slightly more formal tone. "Retain in memory" is another option, which is more formal and emphasizes the act of holding onto a piece of information. "Remember" is a more general term, but one that is still appropriate in many contexts. Additionally, "don't forget" is a more informal way of conveying the same message. Ultimately, there are multiple synonyms for "keep in mind" that can be used depending on the context and level of formality desired.