beginner mistakes is a never ending list because theres so many of them but the most common IMHO are over or under watering,not enough light,disruptions during the dark cycle not enough fresh air or co2 getting into the room make sure that you have a fan blowing directly on your plants it helps them out a lot to have strong and bulky stems and it goes on and on my advice is to go threw the forums again and again because you always learn sum thing new about growing marijuana theres just soooo much to learn but if you can grow some good mj you can grow just abot any thing