The task here is to fold the cloth along its centre line so the fold and the manufactured edges (selvages) are all parallel (see figures), so you'll have a true line to work against.
The reason aligning the selvages (manufactured edges) is important is because you want to cut pieces in line with the fabric's structure, but you can't trust the cuts made by the shop: they're most unlikely to be square or straight because they have to cut quickly, and cutting across 45" or 60" in a perfectly straight line isn't easy if you're in a rush. Your piece will be skewed and/or have a short and a long edge.
- With normally woven fabric, you can use a needle to lift a couple of adjacent threads running from one selvage to the other, and then pull them out, to make an easily-seen line to cut along, and then just fold corner to corner, but with fleece you can't see the individual thread, and with knits you can't pull threads out, so to align the selvages, I fold the cloth in half while letting it hang, and adjust the fold until the selvages hang to the same height:
- Identify the selvages: selvages are the manufactured edges of the fabric (as opposed to the ones the shop made when cutting the cloth from the roll), and can usually be identified by a pattern made by rollers or spiked wheels. These arise when the fabric comes off the loom and is stretched widthways so it can be rolled onto the roll without wrinkles.
- Fold the cloth approximately in half, putting the selvages together. They may be of similar lengths, but don't be fooled - the cloth will be wrinkly if you just align the corners. Grasp the fold in the cloth with both hands, at the edge and about a yard in, and hold it up so the selvages hang freely for the bit you're holding up (let the rest lay across the table).
- Keeping hold of the fold with the little and ring fingers against the palm-heels, use the thumb and other fingers to move the fold until the selvages of the fabric between the hands are both at the same height, then pin the fold nearest the cut edge and transfer what the other hand holds to the free hand, dropping what you've dealt with onto the table (although if you instead hold the last pin against the palm's heel with the little and ring fingers, I find that can help). Take hold of the fold a yard away, and repeat the process. (I normally work over my table, so I can periodically lay the selvages down - first sweeping away from me and then towards me - so I can see how the edges are.)
- You should end up with the cloth folded so the selvages align, which usually means that the shop-cut edges are shown to have been cut diagonally. It's best to cut the shop-cut edges off so the cut edge is square, which prevents you having to remember that there are inches of cloth missing underneath the top layer at the end. You could just cut off the single layer.
When working with a length of cloth, you don't want the extra dangling off the table and distorting what's on the table. I usually fold the cloth in a concertina whose folds are about a foot wide. When I want to work on the fabric, I pull the top few concertina folds from the stack and smooth them from the folded edge towards the selvage.
I found some instructions that said it's best to work with a single layer of velvet, but that if you must work with it doubled, to fold it fuzzy side out because that prevents the top layer 'creeping' along the lower. (Velvet works like a ratchet against itself.) I think this also helps with the pinning.