I like making pillow covers because they are a great beginner project which helps you better understand how to measure and cut (I am currently super bad at measuring and cutting well.) It sounds easy to cut two pieces of fabric or three (if you are making an envelope pillow cover as I like to), but somehow I manage to F it up almost every time. So far I've found it best to cut-out the fabric together. For example, when making masks lay two pieces of fabric on top of each other, trace your pattern, and then use the rolling cutter thingy as I call it, and as most other sewists call it, a rotary cutter. I bought this beginner set (Fiskar's Garment Sewing Starter Set - I would link to Fiskar's directly, but for the life of me I cannot find this on their site) from my local sew shop which includes a rotary cutter, scissor and thread snips.
Also, if you mess up measuring and cutting, you can usually easily fix it by taking out some stitches and re-sewing where necessary. I do it All. The. Time. I did it with this pillow cover I recently sewed:
Somehow I managed to cut the two overlapping back pieces so that they weren't the same size. One of them was way wider than the other. So after sewing, I just cut off the extra fabric on the one that was longer than the other and there you go - looks pretty good to me!
This pillow design was inspired by the few months I spent in the Adirondacks during the fall of 2020 (try to get there is you can - it's magical). My cousin and aunt have been giving me sewing supplies for the last few holidays, and they gave me the green fabric I used for the abstract trees in December. A few days later the idea came together in my head and I scribbled in my journal. This entry was so early in January 2021 that I still was not used to writing '2021' so you'll see I've dated it 2020. I'm a procrastinating sewist, but I actually created this pillow shortly after I dreamt it up!
One of the fun things about creating this pillow design is that I sewed on the green triangles with one of the fancier stitches on my sewing machine (I reference it on the journal scribblings as stitches #13 or 14). It hides the rough edges, so you don't have to fold them and sew the edges to look neat. All you have to do is make sure you stitch along the raw edge. I like this technique for when I have a design with smaller chunks of fabric I'm sewing onto a larger one because it allows me to cutter the smaller fabric into the shape I want and simply sew directly on to the larger piece of fabric. In this case, it was a pillow cover.