For anyone who has trouble with stamina in general and uses keyboard for inputs:
Try hitting the keys more softly. Don't let the hype of the song, the length/speed of the jumps, or anything else make you mash your keys.
No, really. I've been mashing keys too hard since I started and only noticed when I played without my headphones on. As soon as I tried hitting keys more softly two days ago, the entire osu! standard got easier for me. I used to think something was wrong with me. Even after spending weeks trying to improve my stamina and get through faster streams, it barely improved. I would also get tired in the middle of a map with streams no matter what the BPM was. I thought it was just the beatmap, but it was really me and mashing harder than I had to was the reason why. If you're the mashing type, break the habit. It will help you more than you could possibly imagine.