PSA: Do it for us.
PLEASE check your breasts and/or testes each month. (Links are to how-to guides for self-exams).
Remember, this is to become more familiar with your body so you can identify any changes that happen. Its incredibly important that you have a thorough understanding of how your body feels, looks and reacts and whether something has changed over time. Be vigilant and never be afraid to ask a doctor for a second opinion.
Don't wait until someone holds a gun to your head (literally or metaphorically) to begin living your life like you're dying, ok? That means taking care of yourself and appreciating the body you have. Suck every sweet drop out of the moments you have been given. Get moving.