By using Birth Control or not have vaginal intercourse. If you already are pregnant (you formed the question a bit strange) the only way to terminate a pregnancy is by having an abortion at the doctor.
There is no known way to speed up your metabolism. After being pregnant, the best way to lose weight is to breastfeed your baby.
The best way is to not commit a crime.
The traditional way of getting pregnant is by having intercourse - so the best way to avoid this is by refraining from any sexual relations. It is the only 100% guaranteed way to prevent pregnancy.
Despite being nice to your friends and always being there for them, they may still decide to ditch you. For that reason, the best way to prevent losing friends is simply being yourself and having friends who accept you the way you are and really care about you.
The best way to prevent encopresis is to prevent constipation
Eliminating exposure to textile dust is the surest way to prevent byssinosis.
Having vaginal discharge does not prevent you from getting pregnant. It will not expel the sperm. It is not a way to determine whether or not you are pregnant. You can have discharge at any time, pregnant or not.
Hand washing is the best way to prevent the flu.
The best way to stop a girl from getting pregnant is to take steps to prevent the pregnancy in the first place by using birth control. There are lots of options: the depo-provera shot or birth control pill for her, condoms, spermicide, etc. Condoms are your best bet because they will protect her from pregnancy and protect you both from STDs
Don't have sexual intercourse.
No guarantee. But the best way is to have sex with her.
The best way to prevent rollovers when driving is to wear the safety belts and check the tires. One also needs to control their speed in order to prevent rollovers.