Get a prepregnancy checkup.
Discuss your medical history to make sure you're ready for a new pregnancy.
Establish a plan with your doctor to get any chronic medical conditions (such as high blood pressure or diabetes) under control.
Get screened for STDs (including HPV, if your doctor recommends it).
Be checked for nutritional deficiencies, thyroid function, and immunity to infections, like chicken pox, rubella, and whooping cough. Schedule any needed vaccinations now. (Some vaccines require waiting up to six months before conceeiving to avoid risking birth defects.)
Make sure any medications you take are safe during pregnancy.

When: 7 months before conception; this should allow enough time to treat chronic conditions and get necessary vaccinations.