Sound advice there from Mike. If I don't have bathroom scales at hand I stand over the drawbar of the caravan and straddle the coupling. Standing like that, if I can just lift the coupling without too much strain, the noseweight is about correct.
If, as you say, you're paranoid about snaking, perhaps you should take part in a towing course. Not only will they tell you what precautions you need to take to avoid a snake in the first place but also, in a good quality course, you will have opportunity of gaining some practical experience of getting a caravan back under control if the worst happens and it does actually snake. If you react correctly, a snake need not necessarily end in disaster.