If for some reason, you don't have access to Dough's Grid (which sorts underlyings by Implied Volatility Rank or IVR), you can always use the historical volatility indicator to determine the quality of volatility in the underlying instrument. Higher historical volatility equals better premium.
In this particular example, I'm using TLT, whose HV hit a high of 28.77 on or about July 10th. Volatility of greater than 70% of the high is considered pretty good for selling premium, and 70% of 28.77 is about 20.14. Right now, TLT's HV is sitting below 16 (about 56% of the high), so it might be best to wait to set up premium selling plays in TLT until the volatility increases to +20 ... .