I took an architecture drawing class a few years ago and here is what my teacher suggested:
Always Always Always sharpen with a blade! use a small one so that you can control it a little better, but always use a blade! The reason for this is that although it does take some getting used to, you can control how much of your pencil gets shaved off and therefore waste less! you can also control the tip of your pencil... You want to shave the tip of your pencil with the blade (be careful!) and eventually you will have enough control and technique such that you can get whatever tip you need on your pencil!
Also, I personally would not reccomend using any sort of sanding block because you probably do not need one. Keep a piece of scrap paper in your box for testing and you should also be able to use a little bit of that for sanding if at all needed (its always best to test your pencil before using it on your drawing so that at the very most, you can make sure it is at the right consistency and at the very least you can avoid getting "shavings" on your drawing!
Another handy tip for your colored pencils is to have a box for your shavings! My teacher used a cigar box with a rubber strap on it (for sealing purposes and he shaved his pencils into it. I can imagine that someone might be able to find something to do with your shavings if you can't... but he would keep the cigar box with his pencil box and that way he never had to shave into the garbage or anything and he could shave any time he needed to!
That is the blade I use (the one the teacher uses and reccomended)... this blade is magical! It is the easiest thing I've ever worked with and it is generally really good! It appears to be an OLFA stainless steel blade and it is about a centimeter wide! I use it to sharpen and cut everything!
I hope this helps!