That’s a quite a far-reaching question as it does depend on what you want to use your greenhouse for. But assuming you are a newbie to greenhouses and have your very first greenhouse to start growing, the first thing you need is good ventilation. Your greenhouse has a door, which needs to be close fitting and ideally wide enough to wheel a barrow through. It probably has a window or two that open manually, but to get the best airflow in your greenhouse you need vents that open low down and also vents up high to allow hot air to escape. You can buy automatic opening kits that fit onto greenhouse vents and will open the windows when the internal temperature rises, which is ideal if you work or are often away.
Photo: SuperFantastic
Many gardeners have one area of the greenhouse floor to plant into to for greenhouse tomatoes and other hothouse plants. On the other side they have a potting bench and some staging and shelves. Most greenhouse growers will admit that they never have enough room in their glasshouse to grow everything that they want to grow, so space management is important.