Updated: May 17
Jumping spiders don't need very elaborate enclosures. In fact, my grow cups are very small and simple so the juveniles are always within a leap's reach from their prey. They really only roam to find a mate or to hunt, so their needs are easily met within a small space as long as they have enough ventilation, access to food, water, and nesting site.
Jumping spiders prefer to nest on top, so be aware of that when making/choosing enclosures. Lids that are deep or enclosures that are side-opening are great to prevent tearing apart nests built at the top. Enclosures should ideally have a little bit of substrate in the form of paper towels or coco fiber to hold a bit of humidity, and should be changed out regularly to prevent bacteria build-up. If you are feeding crickets or ground dwelling prey (mealworms, waxworms, or roaches), make sure the floor of the enclosure isn't too cluttered.
Jumping spiders prefer some furnishings to crawl on, explore, and web on. But don't make it so cluttered that it hinders them hunting/finding food. Also use common sense. Hot glue anything in place that may tip over and hurt the spider. Don't use anything that may be toxic. Gluing in some fake flowers or decorations for the spider to web on at the top of an enclosure with a deep lid or side door is a great way to furnish without cluttering so much that the spiders can't find food.
Ventilation is SO important to maintain healthy book lungs. Ideally, you want side ventilation and top ventilation. Any water you mist into the enclosure should not create condensation for more than a couple hours on no more than 1/4th of the enclosure. If you have too much condensation for too long, you will need to add ventilation.