[paulca]

The only time I have ever had to double clutch anything is when stationary and the box gets stuck trying for first, you feel it go in the first notch but not the second. It's likely if you have floored the clutch out of good habit before starting the car, but don't lift it again before selecting 1st. Chances are as soon as you lift the clutch it will pop in anyway, but better; pulling it back out of gear, lifting the clutch for a moment and then retrying works a charm. It happens on bikes too. I believe the shaft spins down and the synchros end up in a funny place where without rotation of the box they can't allow engagement. Sometimes on the bike I have just let the clutch out to the bite point and it pops into 1st.

Speaking of bikes, a lot of folks say you shouldn't shift into 1st while moving as 1st doesn't have a syncro, which is why bikes thump into 1st and the whole bike lurches. Personally I ignore this advice for practicality sakes, slowing into traffic going 5-10mph needs 1st gear on a lot of bikes or you will under-rev and shudder the engine. The trick is to do it quickly. If you push it out of 2nd into neutral, delay for a second or two them when you go to push it into first you will get the dreaded dogs clicking and grinding then a horrible CLACK sound as they catch. This is where a double clutching might help.

As to shifting in the car, I just use the syncros with some sympathy. ie. NOT shoving it into gear like a bear, but offering it to the gear and letting it suck it in almost. Seems to work fine, even for 6th to 2nd. 2nd to 6th is a little more 'tender' if you don't let the revs fall first and requires a gentle approach, too much pressure and you'll push past the syncro and grind it.