For many, we take them outside to let Mother Nature nurture them back to a better state of health, knowing that once back inside, they will be in less than a perfect growing location. You may have set them out on the ground under shrubs or evergreens, put them on the edge of the patio or next to the home.
Since the houseplants are not frost tolerant, the best practice is to get them acclimated to being indoors long before we have really cool temperatures outdoors. To start the process, each houseplant should be looked at to see if it is one you really want back in the house. Any plants not headed back inside should be added to the compost bin. Clean up the houseplants by removing or pruning out anything dead, removing any weeds that may have sprouted in the pots. You may be surprised how much they have grown, having had plenty of sunlight, rain and in general from being outdoors. This is the time to adjust their size by cutting back or pinching the newer growth. This will help the transition indoors.
The next step here is to deal with any insects that have found a home on the houseplant or more likely in the soil in the pot. In the plant itself, there could be spiders using the plant as a place to capture their prey or other insects using the plant as a resting site. In the potting soil there can be earwigs, those little armadillo looking creatures that roll up in a ball when disturbed commonly called pill bugs and even ants can set up home in the pot. All these are natural and expected, except we really don't want them indoors. Before resorting to a pesticide, try a forceful stream of water on the foliage to dislodge insects. Try flushing the pot with water which usually drives out any insects that have entered through the drainage holes. If you have found ants, you may need to repot the houseplant by shaking all the soil off and in the process leaving the ants behind. Use a fresh potting soil when you reset the plant.
The last part of the process is moving those houseplants that have been in strong sunlight to locations that are shadier. This will start to get them used to lower light levels that they will have once inside. Ideally, the houseplants should be back indoors before the furnace starts to run. If you need a target date to get this done, use September 30th.