- Being Too Vague: General or unclear subject lines can be easily overlooked. - Overuse of Capital Letters: This can come off as shouting and may be off-putting. - Too Many Emojis: While one or two can add personality, overusing them can make the subject line look unprofessional. - Clickbait: Misleading subject lines may get an email opened, but they can damage trust and lead to higher unsubscribe rates.