Vinyl banners are great at what they do, but people will judge you on them. If they're obviously torn, wrinkled, or dirty, it reflects on your business just as if the potential customer were in your store.
That said, you want to make sure that your banner properly represents you and your business.
When your banners aren't in use, it should be rolled, graphics in, and stored (preferrably in the box it came in) on its end. Laying it flat could cause it to crease over time.
With proper storage, wrinkles shouldn't be a problem for your vinyl banner, but if wrinkles appear, the easiest way is to hang your banner, taut, out in the sun. The heat from the sun will soften the vinyl sign, making it more pliable which the banner's own weight will then smooth things right out. This method of removing wrinkles also keeps your banner doing its job for you with no downtime.
The cleanliness of your vinyl banner is another factor under your control that is easy to handle. Usually, vinyl banners can be cleaned with a damp cloth, water, and nothing else. If this doesn't do the work, use a mild soap/detergent with the damp cloth and then rinse and dry.
Never use any abrasives, harsh cleansers, or solvents on your banner as it may affect the print quality. When done, make sure the banner is thoroughly dry before storing it.
If you keep these things in mind, you're sure to always have a great looking banner so long as it is installed properly...but we'll get into banner installation next time.