I agree with steves. The problem is that, when you look at a relatively large area (say an inch or so wide) covered by narrow planks, your eye immediately notices any slight inconsistency in the gaps between them. A discrepancy of .001" or .002", which might not make any difference elsewhere in the model, becomes horribly obvious.
Sailing ship modelers have figured out over the decades that the most practical way to make really uniform strips of wood is with a table saw - preferably a "miniature" one. With a tool like that, and a simple jig, you can rip out enough planks for the deck of a model in half an hour. But cutting them with a knife blade invites trouble when the blade tries to follow the grain. And it's almost impossible to hold the blade at precisely the same angle for every cut - and if the angle varies, even a little, so does the width of the plank.
Quite a few years ago a fine British modeler named Gerald Wingrove published a book in which he described an ingenious way to make planks. He made a gadget with five or six homemade blades clamped in it, with metal spacers to hold them apart by a specified distance and an integral fence to keep the one on the end parallel to the edge of the workpiece. He'd run this thing along the edge of a reasonably thick, straight board, thereby making a series of grooves in it. Then he'd run a sharp plane along the edge of the board. The shavings from the plane were the planks. I've never tried that trick, but Mr. Wingrove's results were quite impressive. I think Donald McNarry does something similar with his wonderful small-scale models.
It's not so impractical to score grooves to represent planking seams in a thin sheet of wood. (If one plank is just a tad wider than the next one, the eye probably won't notice - as long as the grooves are uniform and straight.) Scored decks - especially if made out of some hard wood, like maple or (my personal favorite) holly - can be made to look extremely effective. Especially if they're painted. Problems arise if a scored deck is stained, rather than painted; the stain emphasizes the wood grain, and makes it obvious that the grain pattern extends across the planking seams.
If I were thinking about planking the deck of a 1/200 battleship my strong inclination would be to bite the bullet and buy precut strips. (Those prices in the source to which steves linked us aren't bad - and the shipping fees, by today's standards, are downright reasonable.) I wish something harder and less fuzzy than basswood was available, but basswood decks can, with care, be made to look extremely effective. Try running a fairly hard pencil around each plank before you install it. (The pencil lead will represent the caulking between the planks - and will survive any sanding or scraping you inflict on it.) When the deck is laid and really dry, smooth it out by scraping gently with a razor blade and/or sanding with extremely fine sandpaper. Then give it a thin coat of some kind of stain, and wipe it off before it has time to really soak in and over-darken the wood. Finish off with a coat of white shellac, diluted almost beyond recognition with denatured alcohol. The shellac will lay down any fuzz that's been raised by the stain - and protect the deck from errant drops of paint that land on it later.
Hope that helps at least a little. Good luck.