I have a simple javascript game and I'm initializing their positions on the y axis using random numbers. How can I ensure that they are reasonably spaced apart? My simple algorithm is:

 y = (Math.random()*1000%600);

However I frequently get enemies almost directly on top of each other. This is a huge problem for the game, since it's a word game and the enemies have text on their center, that if overlapped makes them impossible to kill since you can't see the words. Any advice would be appreciated! I'm pretty new to making games in general so this has all been a learning experience for me!