These need to be accurately made from either rigid plastic or cardboard. Template plastic is not expensive and worth the investment as the template will last longer and remain accurate. Cardboard can become ‘fluffy’ at the edges with use. Some shops will sell template plastic by the sheet.
Check if the templates you are making include a seam allowance of ¼”, some do and some do not. The patterns given in British Patchwork and Quilting magazine are usually full sized. Other patterns may need increasing in size. This can be done on a photocopier or scanner. If printing patterns from the internet, check that your printer is set to 100%. Some home printers default to a lower setting so your pattern will not be the correct size.
In a Nutshell, can be seen in full in British Patchwork and Quilting magazine.