A BH Nymph is indeed a very good fly for lots of fish and I certainly don't want to persuade you from tying it. However, if this is your first fly I usually recommend a #6 Olive, Black, or Purple Wolly Bugger for first time tiers. It is relatively simple and your hook size will keep the proportions correct. All you need for a Wolly Bugger is a 3XL or 4XL hook, thread, marabou, medium chenille, and strung hackle. I usually add weight to my WB but they still work without weight and there is certainly nothing wrong with adding a bead head for a little extra weight. When tying nymphs its easy to get the proportions out of kilter and it won't come out like you wanted. This leads to a lot of frustration and sometimes people abandoning fly tying completely. After you tie a couple of Wolly Buggers you will develop a lot of skills, such as using a whip finisher, that will help when you are tying more intricate flies. A BH Nymph isn't really a difficult tie but IMHO there are better flies to start with.
Dan
Alright fish, I know I got something in this boat you'll eat.....Yep, the 'ol boat carpet seat cushion jig does it every time!