First, check with any friends or relatives too see if they will let you park on their property. If not, check to see if there are any organizations or businesses in your area (or a nearby area) that designates parking lots specifically for people in situations like yours; for example, Walmart allows people to camp overnight in their parking lots. It's not only legal, but the organization might screen the people who use the lot, or even designate a women-only lot. If there are no such lots available, and you live in an urban area, look for streets with no sidewalks, no overlooking windows, and adjacent to woods; the area should be sparse enough to avoid nosy onlookers but populated enough that the car does not stand out. Parking lots of big-box retailers (especially those that are open 24 hours and have restrooms, such as Walmart) are great to clean up in and have security, as long as you spend a couple of dollars there and don't park in one place too often. Parking lots however can be noisy, particularly in the morning as trucks arrive carrying food and goods.   Church car parks are often quiet during weekdays. If you check around, you may find a church that is less used than others. This could be a good place to park, and you may be able to ask for assistance at the church. You might even attend the church to gain rapport, but wait a while before telling others about your situation, and tell only those who seem trustworthy and willing to help.  Industrial estates and business parks are often noisy by day, but very quiet at night. Small ones close to residential areas are best. They have to be quiet at night. You may encounter security in some places like this, but if you are honest, saying you are just sleeping the night in your car, they usually won't bother you. Their main role is to protect the property. University car parks. This is okay if you are a student, but not so good if you are not associated with the university. You may be required to get a parking permit.  Camping grounds are another option,...

TL;DR in Vietnamese:
Tìm nơi đỗ xe an toàn và kín đáo. Mua nút tai.