The first rule of thumb (so to speak) is to use your thumb nail, or any other nail if you like those better. Just run the nail over the scratch, if you nail grabs into the scratch chances are the scratch is through the clear coat, base coat and into the primer or even down to the panel or plastic whatever the substrate is. There are exeptions to this rule, there are times you can feel the scratch with your nail but wet sanding and polishing still removes the scratch.
So what do you do now? Let's start with the best situation and work to the worst. *Always wash and clean the scratch and area around the scratch and dry it off before starting a repair. If you do not know how to use a buffer read the 'how to buff tutorial'.
You have a light scratch and can not feel it at all with your nail.
solution - use a buffer with a light cut pad and polish it out with a light cut compound. Orbital or Rotary would be fine. Orbital takes longer but less likely to burn through any paint. Hand polishing with a micro fibre rag would even remove this scratch with some light cut compound. If you have swirl marks after, go to a polishing pad and compound to remove those.
You have a scratch and can just barely feel it with your nail.
solution - use a buffer with a heavy cut pad and heavy cutting compound, wet sand if needed. This will knock down the scratch and probably leave swirl marks. Once the scratch looks gone use the light cut method to remove the heavy swirl marks from the heavy cut.
You have a scratch and it is definately through the paint, you can see the panel and white of the scratch from 50 feet away!!
solution - wet sand and buff as in situation #2 .. OR .. take touch up paint and apply it in a thin layer into the scratch. Let that paint dry or (flash off). Then use a buffer with a wool pad (wool pads cut alot) and use a light cut polish (add some polish into this compound if you want to help reduce swirls) The heat from the buffer will roll over the touchup paint and cure it into the scratch. To help with gloss of the touchup paint contact Spray King and we can custom mix you your factory color with the binders and flow additives necissary to help metallic orientation and gloss of the touchup paint.