yes it's possible to get a showroom quality finish from rattle cans, although it never seems to b as tough as proper paint so tends to need more regular polishing to stop it going dull.
firstly you need to make sure there's a nice thick layer of lacquer, and make sure it has set properly. i.e a week or so at a reasonable temperature.
also spray on a warm dry day, and try and protect from moisture for a good few hours after it has been painted or the finish may go milky.
then, if the finish has a lumpy / rippled finish, use some fine grit wet and dry paper (i tend to use 1200 or 1500 as it's all i can seem to find locally, 2000 grit would be better for finishing), allong with a bucket of waterand a good squirt of washing up liquid. it helps lubricate the paper so it glides over the paint. be carefull though as it's fairly easy to get a bit of grit under th epaper and start scratching, so keep the area wet and well rinsed.
now you'll probably have a smooth to touch, but cloudy to look at finish. it will need polishing with a proper polish rather than a wax.
for repairs / small areas, and using a hand finish rather than a machine polisher, i've still yet to find anything that works as well as good old fasioned T-cut. go for the standard finish stuff even on metallics as its slightly more abrasive, but the next step gets rid of any swirls it leaves.
then use a normal polish. something like autoglym super resin polish, and top off with a protecting wax if you wish.
i resprayed the rear door on the car bellow using a specially mixed colour aerosol and standard off the shelf halfords aerosol lacquer
