Basic stuff really. How do you cut rolled sugarpaste assume with sharp knife and what? And so many cakes now use circles, stripes etc. It looks simple but in the past when I have lifted these shapes up they stretch and by the time I stick them on its all getting out of sync! Perhaps the thickness is wrong and should I be leaving them to dry overnight? There must be tips but books gloss over this basic stuff.

I have a birthday cake to do at end of April and one layer I want to do coloured stripes.

Your fondant may be too soft. I usually work a little bit of vegetable shortening, some extra powdered sugar and even a little tylose powder into mine before I use it. You don't need to let it dry overnight - you run the risk of having it dry out too much if you do - but you could certainly leave it for a half hour or so after rolling and cutting and before moving the shapes. If I'm not using a cutter, I generally cut with a pastry wheel (a larger one, maybe 5cm for straighter sections and one of those tiny cutters that have the stitching wheel on the other end for more detailed work). If you use something like this, rather than a knife, you'll run less chance of pulling the fondant along with the blade as you go. I also roll my fondant out on a liberal sprinkling of cornstarch, so that it won't stick when I go to lift it. Hope that helps somewhat!

Also, if your edge doesn't look nice and smooth when you're done, you can rub your finger or a little brush against the edge to smooth it.

Good idea, Texas_Sugar!