Generally, just with a plain and unscented soap (to avoid irritating the delicate skin) and warm water. Using a loofah to clean your genitals is best, as since it typically completely dries between uses, it's less likely to attract bacteria than a flannel. Also make sure that you always wipe from front to back in order to avoid spreading germs from around the anus (where they live naturally) forwards to the vagina and urethra (where they don't live naturally), as this can cause vaginal infections and urinary tract infections.
Wear clean underwear daily, go knicker free at night, and change sanitary protection regularly, especially when you're on your period. Ideally, wear a fresh pantyliner in your underwear daily when you're not on your period in order to absorb natural vaginal discharge.
If you prefer to use tampons as menstrual protection, remember to change them at least every 8 hours to avoid TSS, as while rare, this condition is very serious. If you prefer sanitary towels, change them regularly, about every 4-8 hours in order to keep yourself clean and comfortable. (On your heavier flow days, you will probably want to change more frequently.)
Avoid using douches at all unless you're advised to do so by a doctor, for instance if you're given a medicated douche. Douching can end up flushing out all of the healthy bacteria from the vagina, which could result in infections, such as yeast infections.
Hope this helps.