I always blip (double-de-clutch) on the way down the box unless significant breaking is required as I haven't mastered heel-toe yet where a skilled driver is able to both break and double-de-clutch at the same time.
My understanding of blipping (double-de-clutching) is as follows step by step:
1. Come off the throttle
2. Clutch in
3. Take out of Gear (i.e momentarily into neutral)
4. Clutch out
5. Blip throttle
6. Clutch in
7. Put into next gear down
8. Clutch out
All of these steps need to be done in quick succesion and need practice, simply blipping the throttle with the clutch depressed is not doing a lot, you need to do it with clutch out whilst for a split second being in neutral so engine and transmission parts are matching speed. When mastered this will provide a much smoother transition between gears.
Hope this helps. Any old boys out there with pre-synchro experience pleases correct me if i'm wrong.
That's how it's done, I've pretty much always done it (so 10 years now!), my Dad used to do sprints and hillclimbs in his MGB, so he taught me as soon as I had passed my test (and even before, in an old Mini we had when I was 15)
With practice you should be able to get through 1-8 above in less than a second, but start slowly (even parked with the engine off!) otherwise you'll make all kind of grinding noises, and may knacker your clutch by banging it back up with a gear partially engaged.
Not only will it make changes smoother, but is a must if driving cross-country quickly, as you can bomb down a straight in 4th, see a bend ahead that is clearly a 2nd gear job, slow to the appropriate speed in 4th, blip into 2nd (ideally a heel&toe) before the bend without any engine braking then floor it through the bend.
I agree with an earlier post here too, that pedals in the Clio are v good for heel&toe-ing, easiest when wearing narrow trainers.
Nailing a 4th->2nd heel&toe into a bend then flooring it out of the bend is of the best driving experiences there is!