Once your polycarbonate bag does get dirty from regular use, use a washcloth dipped in a very mild solution of warm water and dish washing soap to clean it. Clean the entire shell of the suitcase with this solution and not just the dirty spots. Next use a plain damp cloth to wipe off any soap residue, followed by a completely dry cloth to leave the shell clean and shiny. Do not leave any moisture behind or the stain will be visible.
If your polycarbonate or other hardside luggage is showing scuff marks, use an eraser cleaning pad or even toothpaste with an abrasive sponge to scrub away and buff the area. Finish off by wiping the residue away with a dry cloth.
Brush the surfaces, especially the fabric ones, with a dry brush or broom to loosen dust. Then, use the dusting or upholstery attachment on a vacuum cleaner to extract anything that is loose. Remember to vacuum inside all the little pockets on the interior and exterior of the suitcase. This is a great way to remove the small debris and rubbish that is left behind in the pockets. Remember to feel around first so you don't suck up any missing earrings or cuff links. Depending on how dirty your suitcase is, this may be good preparation for not making more mess on subsequent steps. On the other hand, if removing the dust is enough, you're done.
Take a damp cloth and, if you like, a bit of soap or mild liquid cleaner, and try rubbing gently at a small, inconspicuous area on the outside of the suitcase. If the test is successful, wipe the rest of the bag, changing cleaning cloths as necessary. Follow up with a moist cloth to remove as much soap residue as possible.
If the inside of the suitcase is lined with plastic, wipe it down with a clean, damp cloth (not the one you used on the outside) and, if necessary, a mild cleaner. For fabric, simply vacuum it or wipe it with a dry cloth.
Luggage wheels are the parts that get the dirtiest for obvious reasons. To keep them rolling smoothly, remove any dried soil and loose dirt from them before wiping them down with a soap and water solution. There’s no need to lubricate them if they’re maintained regularly.
For the hardware or solid accessories on your bags, i.e. telescopic handle, zippers, locks and protective edges and bumpers, never use any kind of oil based cleaner as the oil can seep into the fabric or shell of the bag and stain it. Wipe down with soap and water and dry. If there are scratches, buff the area with a fine steel wool scrubber and seal with a protective coat of lacquer or even clear nail polish.
Let suitcase dry thoroughly before storing.
Chances are it lives in a cupboard, attic or under the bed when not in use.
Particularly for softside cases, it’s a good idea to waterproof your bag. When your bag is as clean as you can get it, and especially when it is new, use a spray-on waterproofer to coat the outside. Read the instructions to make sure that your spray is compatible with the bag material.