You didn't cause this and the only preventative is low-dose aspirin, which currently works in about 15% of pregnancies, if you have no contraindications for use.
That means lowering stress, stopping work, bedrest, eating a special diet, supplementing special vitamins, using herbal remedies, cleanses, and just about anything else you can think of to "try", won't actually change your outcomes. That is because these disorders are not caused by lifestlye. Many of us learned growing up that high blood pressure was for old, sick or obese people, people who eat too much salt or junk food, or unhealthy people. That is simply not true, and the type of hypertension we get with preeclampsia is controlled by the placenta. Preeclampsia begins at implantation and continues to be set up through implantation of the spiral arteries in the days and weeks after conception. There is no diet or special protocol that changes that, with the exception of aspirin for some people.
We all want to "DO SOMETHING" and we are willing to "JUST TRY IT, IT CAN'T HURT", but the fact is that you didn't do something wrong that you have to fix, and, sometimes things that are not evidenced-based can actually hurt. Preeclampsia is caused in part by oxidative stress. In the late 90's someone decided that by introducing antioxidants, especially in large quantities, to women developing preeclampsia that we might reverse or stop the oxidative stress. In subsequent research, it was determined that the addition of these antioxidants, like seemingly innocuous vitamins C, E, Cod Fish Oils, and CoQ10, actually made preeclampsia worse, faster. These things were prescribed, especially by midwives into the mid-2000's. Herbal remedies, oils, special protein drinks and other seemingly healthful things haven't been tested in pregnancy and could cause harm. They also tested high protein diets and found those can cause harm to already struggling kidneys of the pregnant woman and cause preeclampsia to get worse, faster, in addition to causing problem for the baby. We talk more about supplements and diets in another unit.
Things you can do:
See your doctor for a physical every year, including checks of:
Well woman checks (pelvic exam, pap smear, breast exam)
Any other routine tests as recommended
Get baseline proteinuria levels
Treat any health issues currently existing (thyroid, diabetes, high bp, etc)
Lose a few pounds if you are obese. It may not prevent preeclampsia, but it is a risk factor, and if nothing else recovery will be easier if you shed a few pounds
Take 400mcg of folic acid preconception
Move your body
Have a a preconception appointment with an OB or MFM and ask if you are a candidate for low dose aspirin
Check with your doctor before you use any natural remedies
Take your meds regularly if you have any
Set up schedule with a therapist if you are nervous about the next pregnancy, or if you haven't talked to someone about the last pregnancy experience. Pregnancy can bring up traumas that you thought you dealt with. At least you will be an established patient, should you find the next pregnancy difficult
Drink plenty of water
Remember that you didn't cause this so be easy on yourself