When a plant has the proper environmental conditions it will thrive.
Every type of plant requires a certain environment to grow strong and vigorous. When growing indoors the environment can be controlled. A green house, grow tent, cabinet or even a converted closet are good choices. The basics are proper temperature, humidity, and air flow. For the more advanced addition of Co2 and odor control depending on what you are growing.
Plants have a certain optimal Temperature range. Grow lights create heat. One simple way is to vent the grow space with a vent fan. A vent fan pulls air in and pushes the air out of an outlet vent usually to outside. Most of the time with this type of set up is enough and considered the bare minimum. For more advanced set up a heater would make the temperature go up. Some time this may be done when lights are off/night time when growing in a cooler space like a basement. An air conditioner is usually used to lower a temperature. A heater and air conditioner are usually not required.
Plants also have an optimal Humidity range. Water will make humidity higher. Venting the grow space is usually enough. If ranges cannot be met a humidify can be added to make humidity go up. To lower humidity a dehumidifier can be used.
3. Air Flow
There has to be a flow of fresh air. A typical set up would be a duct fan or a carbon air scrubber set up that pulls the air from the grow space and vents it(usually to outside. There should be an inlet vent to pull in fresh air. The fan will pull fresh air in and push old air out. A carbon scrubber will remove odors.
Usually having just a carbon air scrubber with fan kit vented outside with a well place fresh air inlet vent is good enough. Sometimes a dehumidifier will be used as well to drop humidity. Keeping Temperature and Humidity in optimal ranges is crucial.