The first factor that will determine where you park is the type of van you use, ie. mini or passenger van, cargo van, cube or box van, RV or camper van. I think that your vehicle should blend in with the area you park, that it looks like it belongs there. For example, I use a 'soccer-mom' minivan, so it parks easily and looks right in place in an urban suburb neighborhood. No one gives it a second glance, which is what I desire. No undue attention. If I tried to sleep in a RV on the same street, the cops would be banging on the door in no time.
I drive around during my daily routine. I go to work, I picnic at different parks, I hang out in different places; where and when I park at night, it's only for sleeping. Before I go to a night sleep spot, I am prepared and ready to do just that. When I park my van, I try to minimize the lines of sight from houses, so hopefully, they can't watch me getting in and out of the 'back'. My van has all the privacy panels up and my bed is prepared to jump right in. I don't get out of my van, I just quickly slip into bed, when I think no one will notice. Because of prying eyes, I don't want to give anyone a clue that I am sleeping there, so, I try to minimize any moving around or noise, I just read a little and fall off to sleep. In the morning, I take a quick peak around to see if anyone might notice, then, I get in the front and drive away.
I generally go to bed around 10 pm, and get up around 6am. Most people are getting dozy that late in the evening, and they usually aren't up or wide awake that early in the morning. That way I slip in and out, of any particular street 'block', usually undetected. If someone notices my van in the evening, I'm already gone first thing in the morning, so they forget about it. I also don't use the same block, night after night; I don't like to go back again to the exact same block for at least a month. That way, I don't become a focal point for any concerned, blockwatching citizens. I like urban 'blocks', that have most of the houses, split up into apartments; in those areas, there are lots of people coming and going, and lots of vehicles parked in the street. Perfect for my style of night parking.
Although this routine is really a lot of effort, it becomes second nature after a while. In these areas, I feel safe with people around, and my van blends in with lots of parked vehicles, reducing the possibility of someone wanting to break in or steal it. It's usually pretty quiet at night, but, in the city you are going to have some noise; you get used to it.
Sometimes, I utilize a parking lot. I know of two pay parking lots ($2 fee, 6pm to 8am), where there is no night time attendant, they are fairly safe, and you can get in and out, 24 hours a day. Walmarts in this area, still allow overnight parking, good for a occasional night. Sometimes a shopping mall, with no overnight parking restrictions, can be used carefully. But, because there is little or no other vehicles around at night in most lots, I feel you stick out like a sore thumb. A target for thieves or cops/security to hassle you.
On the weekends, I'm gone out of the central city area, to go adventuring or visit family and friends, parking in their driveway, etc. When I return to work, I drive into the city on Monday morning, so I usually only have to stealth park four nights a week.
Whenever night parking, I use my 'gut' feelings, when judging a potential spot. If it doesn't feel right, it probably isn't, so go somewhere else. There are so many choices, and it's usually easy to find a better one, just down the road.