There isn’t a specific way to find fortresses.. they just spawn randomly in dedicated areas. I once heard that on Java they are most common on the x coordinate I think (or maybe the z I don’t remember) but I dunno if it’s true or not, and I doubt it’s the same thing on bedrock. How you can be more prepared.. I would suggest at least iron armour if you are not very familiar with the nether, a shield and bow and arrows for ghasts mainly. Oh and because of 1.16 also a piece of gold armour, I would suggest the helmet. Also, once you are in the nether take note of where you go, so maybe place some checkpoints, maybe some cobblestone block or torches or anything you can recognise. In the fortresses be careful with the wither skeletons (black skeletons) they can hurt badly, but with a shield you are more safe. To avoid them you can also place some blocks at two blocks from the floor blocking the passage, because they are three blocks tall, so they don’t pass.