1- knit a parallelagram..
(cast on X, with a strechy cast on. knit flat (in any stitch),
increase every 4 row both ends.
when knitting is about 3 inches long, bind off.
sew sides seams, at top (cast off edge) and at bottom(cast on edge) leaving seam open at side. (for finger loop of mug)
2--or you could cast on, join into round work some rounds, (increase 2 times in every 4th round) for about 1 inch
then work straight, (not rounds) for 1 inch,
then go back to working in rounds for 1 inch and bind off
3--or you could cast on 8, join into round, work in rounds, increasing 8 stitches, evenly, every other round, till the flat is about equal to diameter desired. then work in rounds, for 2 or more inches, (increasing 2 stitches every 4th round,
if you want a tall cosy (for a mug) work an inch flat (turning work) to created vertical hole for finger loop, end by working in round again.