The reason for blipping over the correct rpm is that it takes a little bit of time to get the clutch out once you have blipped. Gregs advice is spot on as always, as it is best to learn how to downshift to a given gear and rpm before experimenting. After sometime you will develop the feel for how much to blip for a given shift, and the numbers wont matter. Until that time, blip for the numbers that you remember.
When I blip the rpms go over where I need them to be, and then I pull the clutch out while the rpms are falling to the correct rpm. Do what works best for you, as I know some people who like to catch them on the way up, but I prefer catching them on the downswing.
If you shift, get it in the lower gear and then blip, I recomend sitting in the driveway with the car off to practice the motion. What works best is clutch in, then blip and shift at the same time. By sitting the driveway with the car off you can get used to the motion better, and at some point it will be second nature. You dont have to do this, but it saves time and is IMO easier.
There are quite a few great threads on this, so doing a search might help answer some questions. Hope this helps!
:cheers: