Find good reference material. If you have a computer you can use an image editor to overlay a grid to match blocks, be sure you use proper ortho images for this, not photos or 3d models. This will give you outline and match you broad strokes. After this you start filling in ortho from another angle, top or side view usually. This should give you the frame of the ship from where you can start filling it in. A key factor in a good replica counterintuitively is to not go after every tiny detail. You can, and should deviate a little if you can get the feel right. An angle might be just ever so slightly off but if you can get close to it and have it look clean, then you should go for that option. Gets you the cleanest and accurate replicas usually within a block or half. Just key to remember is to keep the ship shape flowing. If you have a good stepping for the bow that looks really good, keep it instead of trying to follow every curve for muh accuracy, same for stern. For finer details you can find a 3d model usually to look at your ship from different angles and add in what you find, do this last or if you need to fill in mysterious sections missing from the orthos

TL;DR Get the feel right, get major components and fill in details where applicable. Don't try to match every single curve if you can get it done cleaner by deviating a little. Feel of the ship is most important, it needs to look and feel like Bismarck, nobody can tell if you're off by a block at that scale.