Minecraft Speedrunning/Nether Fortresses
Nether fortresses are one of the essential structures since they are the only places you can find blazes which drop blaze rods which are essential to beating the game.
Each nether fortress spawns with two blaze spawners or blazes can spawn naturally around the fortress. Each blaze has a one out of two chance of dropping a blaze rod when killed by the player. To be safe, you generally want seven or eight blaze rods but can leave with fewer if you're pushing for time. These tend to be quite dangerous since wither skeletons roam the fortress and blazes can snipe you from quite a long distance.
There are two sections to the fortress: the chest section which has walls and a ceiling on the corridors and the spawner section which is more open with the two spawners. The chests can contain some useful stuff such as iron, gold and obsidian but mostly they won't be that useful. You want to find the spawner section since the spawners are generally the faster way to get blazes. The wither skeletons are more than 2 blocks high so blocking off sections of the fortress can be useful to ensure you don't get ambushed by them. If you have a fire resistance potion you should use it since it nullifies all blazes' ranged damage, although they can still melee you if you get too close. If you don't have fire resistance, using a shield can help to protect you although you can still get from behind and the shield doesn't cover your whole hitbox. Otherwise you should try to dodge the blazes' shots since blazes shoot three shots then have a cooldown before firing three shots again. Learning blazes' attacking patterns will help you to kill blazes without dying. Other tips are having plenty of food to regenerate health if you do get hit and using blocks to block blazes' shots.