I have been trying to make bread using a bread mix and my mixer.  I read that the amount of water you should add can vary on the humidity at the time.  The mix instructions say that I should add 300ml of water to the mix but I find that by the time I have added 250ml it is already quite wet, so I never add the full 300ml.  There are no instructions on how long to knead the bread if using a mixer but a recipe for bread in my mixer book suggests around 5 minutes.  I have done this but I think that maybe it needs longer.  My question is:  Could my bread be too dense and moist due to:  Too much water? Not enough kneading? Not leaving it to prove for long enough?  What is a "warm place"?  How warm is warm, without killing off the yeast?  As you can see, I'm quite a beginner with baking! 
I make bread a couple of times a week and usually have light fluffy results.  On occasion though, I end up with dense and fairly wet loaf. This usually happens if I have been lax and not made it in a while and haven't bought new flour/yeast. It's important to keep (dried active/instant) yeast in particular in a sealed container and observe best before dates, else it will not work as well as it should.  Make sure your bread mix is fresh and well before the best before on the packet.  It's difficult to describe the consistency of a well kneaded dough - there's really no substitute for finding someone to walk you through it so you can literally get a feel for the texture of dough that is ready. If you have any friends or family that bake their own bread to results that you are aiming for, especially if they use the same mix as you, ask them if they can show you how they do it and get your hands stuck in.  For a warm place in winter I usually set my bread for proving in a bowl by a radiator in my living room. 