How to: Sram 2x10 to 1x10
If it's a mountain bike, you could use a chain guide like this one. The rollers keep the chain aligned on the chain ring at all times and the rear provides tension as it normally would. 



NB: I'm not necessarily recommending this one in particular, just it or something like it. I have no experience with this particular model. 

I'm not sure if they make anything comparable for road setups. I wasn't able to find anything with a quick Googling.