A blood test can determine your LDL ("bad") cholesterol, and should be done starting in your 20's, and every year after if it is abnormal, or every five years if your reading is normal. Have your blood pressure checked every year if it's high, or every two years if it's at or below average.
This essential test helps to detect cervical cancer at an early stage, when the recovery rate is very high. Additionally, start getting tested for HPV when you are 30, and then with your Pap smear every three years. HPV is the leading cause of cervical cancer, and many sexually active women contract this infection at some point. It is tested using an HPV DNA test, and can use the same specimen as the one taken for your Pap smear.
Some doctors are still abiding by the old guidelines until more studies prove that upping the age of getting tested doesn't result in more fatalities. No matter what age you start getting tested, ACOG recommends giving yourself monthly self exams to look for any lumps or bumps that weren't previously there. Visit cancer.org for a detailed guide on how to do a self exam.
Get checked annually, especially if you have a family history of skin cancer, and semi-annually if you've been treated for melanoma.
Additionally, conduct a self exam for any new or suspicious looking moles on your body. The American Academy of Dermatology recommends using the ABCDEs of melanoma with instructions on what to look for and an illustrated document.
Chlamydia and gonorrhea can both be tested by doing a cervical swab; a blood test can detect HIV.
Lead a healthy lifestyle and set a good example for your kids by eating plenty of fruits and vegetables, getting regular exercise, and refraining from smoking, excessive alcohol consumption, and other unhealthy behaviors.