There are different paints I generally stick to rustoleum for metals or for High Gloss I hit up the Auto Parts stores. I have used Dupli-color paints several times and I have always gotten good results.
Now to get good results you need to do the following.
1 Sand and prep the surface. Do a good job at this. While sanding look for any imperfections that you may need to touch up. Sharp raised edges around cutouts, small dings or deep scratches. File/sand the sharp edges down flush and a little bondo goes a long way to making things look nice.
2) Wiping it down. Wipe it down with lint free cloths and alcohol. I don't recommend anything stronger. Why? because you generally don't know what paint they used and a stronger solvent may cause the paint you didn't sand off to become tacky and smear.
3) After drying wipe down with a tack cloth. I know you used lint free cloths but trust me there is still dust and fibers there. Don't rub hard just a light wipe over the entire area.
4) Primering- I highly recommend giving your paint project a good coat of primer. I recommend sandable primer just in case you mess up and get a drip. Now is a good time to perfect your painting technique as well. Since primer is much more forgiving then paint.
5) The primer dries pretty quickly in most cases in under a hour. Take the oppourtunity now to look over the case again. Painted a different color gives the case a whole new perspective to your eyes and you may see something you missed.
6) If you sanded it or worked on it at all. Wipe it down with alcohol again and a tack cloth. If not wipe it down again anyway. I have had more then a few hairs or dust ruin an otherwise perfect paint job.
7) Painting- When you paint. Do it in a ventilated and well lit area but keep it shielded from any nasty outside dust carrying wind or other nasties. So before you paint clean up your area well and dust and vacuum if need be. You will regret it if you don't
8) Maintain the proper distance from the case as instructed on the can. Paint in light coats. I generally do the first coat up and down wait a few minutes. Then the second left to right. This ensures good coverage and you not going over the same aread twice in two heavy coats. Be in a comfortable position when you paint. You don't want to move around too much if you do you may forget where exactly you left off giving you a heavy or thin spot in the paint.
9) When you are finished with the coat give it a good once over to look for any areas you missed. Then close any doors you have open and leave the area immediately. No sense hanging around checking out your work as a piece of lint or hair from your shirt or body drops off into the paint.
10) Additional coats.It is basically the same all over again except this time you scuff sand with fine sand paper, wipe it down, tack cloth, re-coat.
Keep the coats light and consistant and work in a well lit area.
That should help a little bit.
I really cannot stress the importance of the .99 cent tack cloth. Trust me no matter how good of a lint free rag you use you will still leave lint and dust behind this has been the difference in the past between an Ah **** and a good job.