Downshifting by the Double-Clutch method just takes practice. My suggestion is to just start off by double-clutching your upshifts. In every manual that you drive, just keep hesitating in neutral and depress and release the clutch. Once that pattern is down, now just apply the same method in reverse, only this time while hesitating in neutral with the clutch out, just give it some gas. The hard part is, just how much gas to give it. When you are rolling slow and need to downshift, a little tap on the gas is all that's necessary, but the more speed your rolling, the more gas is needed. There is a kind of a narrow window as not enough gas and too much gas will both make it grind. Also some transmissions are harder to downshift shift than others. The greatest importance of downshifting is to put no strain or "lugging" on your engine. The only alternative is to pull over and start again, as mentioned above.
Bill
