Schhtopp! Thishh car ish not ready for washing yet! It’s covered in meteorite sized lumps of muck, a carpet of road grime and the remains of a less-than-sonic hedgehog.
You really want a pressure washer for the pre-wash stage. Even a cheap one is better than a watering can or piddly hose attachment. If you live in a flat, then a watering can with an open spout or a bucket of water to slosh over your car are probably your only options.
Get the car wet… you want the dirt to be lubricated. Water is one of nature’s great natural lubes (no sniggering). Now try and remove as much stuck on grime and dirt as you can, without actually making contact with the car. Let the water do the talking.
Watch out for vinyl edges or areas of flaking paint. A good pressure washer will have these lifting in no time if you’re not careful. Don’t get too close to the paint with the pressure washer lance, jet the panel at an angle and never jet into the ground.