The best way to touch up?
Using too little is better than using too much. Use a cocktail stick to till in minor imperfections... right in the cracks of the chip/scratch.
Using too much is only going to ruin the look.
Then after you've "filled" the scratch in, laquer it on.. Then wait for it to dry and for that really good look then you'd need to wet sand it and then compound it back up.