Usually, playing intense level maps and up requires you to "keep your cool" even more. Just some simple mistakes/habits can make it a living hell. Well, here's my thoughts on how one can improve by putting these into consideration....
1.) Tensing up too much during game play => WILL wear you out fast and gives your hands a very unpleasant feeling after a few plays. This can also slow down your reaction time and accuracy [from moving too stiffly].
2.) Panic or getting nervous during game play => This can screw you up badly with accuracy and focus if you crack under unnecessary pressure. Being too nervous can increase the rate of mistimed hits and cause you to aim all over the place since you're not able to properly focus and control the cursor. This can also make you too tense, decreasing your performance even more.
3.) Large amounts of focus on so little area => Putting too much focus on just 1/4 of the area of the playfield could make you "blind" or unaware of the next set of notes or jumps, making it feel more unexpected than being mentally prepared for it. Being taken by surprise can also make you feel more nervous.
4.) Playing in rage => If the map is kicking you in the rear, come back to it later and play other maps. Playing upset won't help and only makes you burn yourself out quicker.
5.) Put yourself in the mapper's shoes => Learning the mapper's base style used for creating beatmaps can help you focus better by knowing what you're up against. Also, learning more about the song itself can help you point out the beats used more accurately.