'Hoy

Do you guys think it's a bad idea to be writing more than one story at a time? I'm writing my first story but have ideas pouring out of my head for the next one. Not a sequel but a new plot with new characters, do many authors on this site handle two stories at once? The only ones I've seen are collections of oneshots which are simple, I want to manage two fulllength stories. I don't know if it's the best idea so please help send me in either direction. I just want to know if anyone has managed multiple stories and actually done a swift job of completing them. 

Kwa Heri