This is the easiest one to start with. I made a wee set of clothes for Simon: some black jeans, a striped t-shirt and a sweatshirt hoodie, all from spare fabric left over after making similar pieces for James. Here are the two of them working at their computers.
And here are some close-ups. They were based on commercial patterns (Simplicity), which I think are designed for 18" dolls. Simon is only 16" tall and quite a lot smaller all round, so the patterns had to be reduced in size quite a bit. The jeans were quite different from the pattern in the packet since I added real pockets including a coin pocket, silver top stitching and a velcro fly. They fasten with a press-stud. The fun part is how quick and easy it is to knock dolls clothes up - and it reduces the piles of <1mx<1m pieces of fabric.
I also have some tartan fabric, so cut off a bit to make a great kilt for Simon. I actually ironed and hand stitched in the pleats, which isn't the way a real great kilt is constructed - you are supposed to fold it into rough pleats each time you put it on. This isn't really finished. Needs a shirt to go underneath it. I also have since bought some shoes and boots for the dollies. Unfortunately I don't have a picture of James in his great kilt for comparison.