Many pieces of material have a good and a bad side, try and remember to make the outside of the garment of either one or the other. As you become more experienced with the material, you will be better at spotting this. I find the best way to avoid making this mistake is to fold your material in half, lay all of the panels of your garment out and cut two pieces at a time, then pin them all together and start to sew.
Lay your material out on a flat surface, pin your pattern to the material and then carefully cut around your pattern (make sure you have left a seam allowance on your pattern). Always cut with sharp scissors, preferably with material scissors as they are much better. It will reduce fraying, give your garment pieces a crisper edge and be easier to cut.
When I bought my first piece of material, I got a real bargain and I bought way too much – 8m for a dress! (You normally need 3-4m). I kept looking at it and panicking about cutting into it and messing it up. I found that material so intimidating due to the possibility of my wrecking it, I wasted months not cutting into it. I eventually decided that the material was wasted anyway by me not using it, so I began cutting. The dress was my first adult experience at sewing, pattern making and medieval dress; it was not brilliant but it was a start!