Having a baby is a huge step for most of us. Check out this great planning worksheet from the CDC. You can complete it per your own goals and make a custom plan for yourself and your family.
If you can manage it, consider getting a medical check up to ensure everything is alright health wise.
Planned Parenthood has some detailed and good information on pre-conception health.
If you are on a tight budget and have some medical insurance, ask your medical provider to write you a prescription for generic prenatal vitamins. Stores like Target, Walgreens, etc., provide discounts even on generics.
Also, learn more about WIC (a federal program) and see if you qualify for assistance from the WIC website here.
Check if you qualify for Medicaid, more information here.
If you have insurance please look up a good Ob/Gyn in your network who can advise you on and provide prenatal care.
If you do not have medical insurance, check to see if you qualify for Medicaid, more information here.
If you do not qualify for Medicaid, see if to locate a community health center near you, using this link here.