I've been told that when you shift without the clutch, you have to "listen" to the engine to tell when to put it into the next gear. What do you 'listen' for?
(They say in the low boy I might be driving, you really don't have time to double-clutch, because if you don't hurry up and shift, it will slow down so that you're either stopped or going to slow to shift into the next gear)