One of the best ways to remove scratches and grime is help make sure they never appear in the first place. Wash your car once a week at least. Allowing dirt and grime to build up can lead to extensive paint damage. Make sure everything you use to wash your car is thoroughly clean and free of dirt. Dirt on a sponge is the number one cause of swirl marks. Keeping your car clean and waxed also prevents road grime and bug bits from adhering directly to your paint, making them easier to clean off.
There are several car care products out there formulated specifically to remove grime, sap and crushed insects from your cars paint without causing any damage. These products work wonderfully and most are inexpensive. Don't use harsh soaps like dish soap. After removing the grime, your finish will require a reapplication of wax. If you don't feel like taking the time to wax your car, you can use a spray-on wax. These products make excellent temporary protection between full wax jobs.
Much like road grime, there are products specifically formulated to remove light scratches and swirls from paint finishes. Follow the directions on the bottle and be patient. Often, removing swirls and scratches, especially from large areas, can take up a whole afternoon. Swirl remover is essentially low grade paint thinner, so be sure to apply it to the cloth or sponge you'll be using and not directly to your paint. Avoid polishing clear through to your primer. While this would take some effort, it is possible.
It is almost impossible to avoid light scratches and grime on cars that are used regularly. Smashed insects, unclean sponges, bird droppings and road grime can all cause scratches in your paint. Even using drive-through car washes or washing your car with sponges that are even the slightest bit dirty can cause unsightly swirl marks. Luckily, there are several products available that will remove these swirls and grime from your paint.