You don't need that clean car smell, but it's so nice to have a freshly washed car that's been vacuumed and detailed. Except who wants to spend $150-250 to get that done?
First, gather up the equipment. You will need a bucket, a good cleaning solution, a very soft, natural sponge, a squeegee, cotton swabs, a high quality liquid synthetic wax, cotton swabs, a vacuum cleaner, dust clothes, and lots of either all cotton cloths or microfiber. You don't want anything with polyester in it as that will scratch the paint. Chamois cloths can also be used but tend to be a bit more expensive. If you have leather or vinyl seats, get a cleanser just for that, otherwise, use a spray on, vacuum off cleaner for cloth seats.
Some people use two or even three buckets for washing their car. In the three bucket method, one bucket is just water for rinsing off the sponge. The second bucket has a soapy solution for washing off the sponge to remove grit and dirt. The third bucket is another soapy solution for using to wash the car. So for each pass on the vehicle, you would get soaped up, wash a section of the car, rinse off the sponge, wash the sponge by dipping a few times and squeezing out the dirt, and then getting more good soapy suds and wash another part of the car. The two bucket method is similar but it's just water for cleaning the dirt and grit off of the sponge before getting more suds.
Park your car in the shade or at least as shady as you can get. Set up your boom box and get the tunes playing. Open up the hood and clean out the leaves that accumulated. If you have a trunk, you'll do this as well. A good shop vac will take care of this quickly, otherwise, carefully use your hands.
Secondly, starting from the front and working backwards, hose down the car and get to work washing. Pay special attention to removing bugs from the grill and headlights, and any sap that might have fallen on the top of the car. Rinse really well getting underneath the car as best you can. Rub your hand over the paint. If it feels smooth, then start squeegeeing the windows. If it doesn't, you may want to wash again, and invest in some detailer's clay to remove everything before you put on a coat of wax.
The first thing you want to dry are the mirrors and the windows since they dry the fastest. When drying the body of the vehicle, try to use a blotting motion rather then rubbing. This saves on your paint job. Change towels frequently so you're not rubbing dirt onto paint. And make sure you use a separate towel just for the wheels. They tend to be the dirtiest and you don't want that grease back on your nice clean car!
Third is the actual detailing! You need to make sure that the car is completely dry before you put on the wax. So at this point, you could wash the insides of the windows and the rear view mirror, and vacuum out the floor and mats. Then if you have cloth seats, spray them down with the cleaner. Using a very soft cloth and following the directions, apply the liquid synthetic wax to the car from front to back. Make absolutely certain you avoid anything plastic, metal, or any of the trim. It could take hours to get it off, so be careful up front. Synthetic waxes last long, and liquid waxes are much easier to apply. While it's drying, you can vacuum off the cloth seats or you can treat the leather or vinyl seats. Using your crevice attachment, vacuum out all the little areas around the seats and any storage areas. Wash down and dry any spills in these areas. Taking the duster, dust down the dashboard. There are special conditioners for dashboards that keep the material soft. It's your call if you wish to use them. Use the cotton swabs for cleaning out the vents. Using a damn cloth, wipe down the steering wheel and the steering column. A lot of dust gets trapped here.
When the wax is all dry, it's time to buff. Start in the front, use a back and forth motion with a very soft cloth. Do not use the circular motion as it will cause abrasions in the paint surface.
Now sit back and admire your work. Great job! Do this at least once a month to keep your car in perfect condition. If you have external problems like sap, salt, leaves, and messy birds, you may wish to do this every other week.
If you did this to sell your car, you can keep it looking great by parking it carefully and wiping it down with a soft microfiber cloth before you take it out for a test drive. And I'll leave it up to you whether you use New Car Smell scent.