For those folk making masks or face coverings, I have been following the www.bigcommunitysew.co.uk tutorials and patterns. check out some links below and look on the tutorial page for some ideas and help.
shaped face cover instructions
Below is my version of a rectangular face covering. Any questions then do shout!
cut a rectangle 8 inches by 14 inches long. 
sew the seam and move to the middle 
at 4 and 10 inches, pin and sew your elastic ears 
fold back up and stitch the sides . don’t forget to leave a gap for turning! 
turn it all inside out 
pleat and sew your folds, being careful with that much fabric under your machine 
pull any threads through with a pin, tie and cut loose ends 
ta da!