I've gotten to the point where i have LDs fairly often now (mostly DILD, usually about 4 or 5 a month) but they are usually very short and i don't get to do any of the things i really want to do in them .

Is there any reliable way to make your LDs longer or more vivid?

Also, is there any upper limit on how long you can dream for or is that only limited to how good you are at it?

I've heard stories about people dreaming for days (dream time) and even one about as monk who dreamed for 100 years, i don't know if they are true or not, the longest LD i ever had was about 5 or 6 minutes long dream time and even though it was pretty awesome i think if i had more time i could do a lot more and have even more fun.