Park it after dark and leave before it gets light to avoid drawing attention to yourself and your situation. Crack the windows to allow moisture to escape so you don't steam up the car windows — a HUGE sign someone is sleeping inside. Park at 24-hour stores like Walmart, SAMS Club, and truck stops where other people are also sleeping in their vehicles. Park in apartment complexes or on the streets outside an apartment complex. Some apartments require a parking sticker or have assigned parking places. Look for signs of stickers and decals and avoid those complexes. Anyone can park on the street.
It's a car. You're sleeping in it. Don't decorate it like your bedroom. Keep it simple. A sunshade on the dash is okay, but don't hang curtains and towels and crap around the inside. People rarely look at a car unless it stands out. Just don't stand out. When you put up curtains etc. in a car, it shouts, "I'M SLEEPING IN HERE!!" If you have to "change clothes" do it in a gas station bathroom. Once you decide where to park for the night, don't get out of the car once you park. Slaming doors, moving around etc. attracts attention. If people are looking at you sitting there, then pull out a map and a cellphone and look like you're lost.
Don't "set up camp." Meaning, don't hang out in your car reading or playing Angry Birds on your cellphone or whatever. Don't put out a chair and barbque grill (some folks do!!!). Don't sit on the curb to smoke, or eat, or drink. Just pull up, lie down, sleep. Get up and MOVE the car and park somewhere else before it gets light or as it gets light.
Get a sleeping bag to sleep in. They're $25 or less at Walmart. No towels and blankets and comforters and all that crap. Sleeping bag. Pillow. ONE towel. Put the towel over your head to hide the fact you are a person sleeping in a car. If you have a bunch of personal stuff because you're living in your car, put as much of it in the trunk as you can. Put everything else in storage bins. Put the bins on the floor boards or seat and sleep on top of them. Better yet, get rid of all that stuff. Store it in a small storage unit ($50 to $100 a month) or put it in bins and ask a friend to watch it for you.
Places to sleep during the day without getting hassled are parking garages. You may have to pay ($5 to $20 in larger towns, free in most small towns) but it's cool, and much safer if you do and you park somewhat close to the entrance and not in the bowels of the garage. There is a lot of noise, but hey, you're not likely to get hassled. Hospital parking lots (Emergency room lots), Churches ( with their permission), construction lots (talk to the foreman if you're a guy with a truck. Some will let you park there as a security measure if you seem honest, clean and drug free.)
24-hour fast food places are NOT good places to park because they will call the cops if you're there more than an hour. If you ask the manager, explain you're traveling and just want to rest for 4-6 hours before getting back on the road, most will let you park there, especially if you show them your driver's license to show you're legit.
Any street, cul-de-sac or neighborhood with multiple cars in the driveways is a good place to park. Again, arrive after dark, leave when you start hearing other cars leave. If you can get a night job and sleep during the day, you're much less likely to be hassled. Find a nice bar or restaurant, like something at a hotel that's open to the public. Don't park near the door. You can usually sleep there with no problems until the bar closes - about 2-3:30 a.m. and sometimes even afterwards. If you sleep near a bar, TAKE THE KEYS OUT OF THE IGNITION, especially if you've had a drink. If your story is, "I had a few drinks and am sleeping it off," expect to get rousted to walk a line and prove you're not drunk. Some states will charge you with drunk driving if you have the keys in the ignition even if the car is not running.
Any other time my advice is to LEAVE the keys in the ignition (or A key) so you can get up and get out quickly, without having to find the darn keys if you have to.
Learn to "cat nap" and sleep 2-3 hours in different locations. Never park in the same spot two nights in a row, no matter how great a spot it was. Police look for patterns, so don't develop any. If they know you park somewhere every Friday, or Monday, they'll be there when they're bored, rousting you up and out. It's not fun. It's a pain to find a new place every night, but do it.
If you're told to leave, then leave. No arguments, no attitude, no "I have a right to be here BS." Apologize, thank them and MOVE immediately!! Then NEVER EVER go back. Going back means you're trespassing and they can arrest you the next time.
Do not sleep in business parking lots — especially those with signs saying "no parking." They will tow your car, even with you in it, and you're most likely to lose the vehicle because of the insane cost of getting it out of the impound.
If you MUST sleep in a business parking lot, make it an auto repair place and make sure you have work done there the next day, even if it's just an oil change or you buy a part.
Most grocery store lots are patrolled by security. Buy something in the store and leave the bag on the front seat. You're a customer, you have a right to be there. It may just get you ousted instead of arrested.
If you are a veteran or a member of some club, check with the Elks, or Moose Lodge or whatever and ask to sleep in their parking lot. People like to be asked.
Do not leave trash, use the bathroom in the parking lot, or leave any evidence that you were there. People notice. Pick up any trash around your car/vehicle. Be friendly. If people ask what you're doing there, tell them. Be honest as you can, or have a good story. "I had a fight with my boyfriend/girlfriend and I just needed to get away for the night and didn't have enough money for a hotel." Or, "I'm traveling through and just wanted to take a nap." Better to tell the truth than invent something.
Cops have awesome bullshit meters and if you lie they'll know it and think you're up to no good. Better to say, "I'm homeless and don't have anywhere to sleep tonight and I thought I'd crash here, but if that's a problem, I'm happy to move on." works much better than anything you can invent. They just don't want troublemakers, criminals or thieves on their beat. Once they figure you're compliant, not a troublemaker and willing to cooperate, most will leave you alone, or tell you where you can sleep. Be polite. Lose the attitude. They can be your best friend if you're on the street and in trouble. But it all depends on your attitude.
Safety tips:
Get some bear mace. Keep it close and know how to use it.
Lock your doors. Keep your windows rolled up no matter how hot it is. Crack them one inch, but no more, to let condensation out.
Sleep in your clothes. If you're rousted by cops and get out of the car in your underwear, or worse, naked, it doesn't look good and things will go downhill from there.
Sleep in your socks, but not your shoes. Buy a cheap pair of slippers and keep them on the floorboard on the driver's side. It's illegal in some states to drive barefoot. Just being IN a car can be construed as driving without shoes.
Use the bathroom, eat, pack and sort and all that "housekeeping" stuff you need to do in your car/out of your car before you get to your parking place for the night. If you have to get the sleeping bag and pad out of the trunk, then pull in somewhere and do that. Set up the car for sleeping so all you have to do is climb into the back , or lay down your seat and get into the bag to sleep. The less attention you draw to yourself, the better.
Get one of those loud air horns - the annoying, ear splitting kind used at football games. These are two things you can use to draw attention to yourself and defend yourself should someone try to break in. Thieves mostly don't want to draw attention.
If you have a gun and a permit - awesome. Have them handy. Be aware of ALL the gun laws in the state, the county and make sure you are NOT on federal property even if you have a registered and legal gun and permit. When the police ask, "Do you have a weapon," your first words should be, "Here's my wallet, and my permit," and your next words should be, "The gun is ....." and a description of where it is. It's better if you're outside the vehicle when this happens. It's not going to be nice no matter how much you would like it to be. You can only hope the cops who are stopping you or rousting you are reasonable and understanding. Don't lie to them. Anything you say CAN AND WILL be used against you.
If you sleep in a truck stop, expect to be awakened by prostitutes knocking on your window. Cops will shine a light in the window. Prostitutes don't.
If you sleep in a truck stop, park near a large structure, island or near the stop itself. Little cars with no lights are hard to see by sleepy truck drivers who aren't expecting you.