I think for most people that are struggling to find their mojo, frumpy can be avoided. Some of the following may help:
Look on Pinterest, Google etc for outfits, styles that you like.
Ignore any mention of mutton and wear what you like.
Decent hairdresser, diet, a bit of exercise, some grooming.
Clothes that fit and are your new style (maybe a touch of rock chick, hipster, classic, preppy etc basically anything but frumpy). Get rid of clothes the moment they become tatty, dated etc.
The right size underwear.
Footwear can be a minefield of frump- no Cornish pasties, crocs etc. This also applies to summer clothing- choose carefully.
Treat yourself to a really lovely jacket or coat.
Take a stylish friend shopping and be fussy, never buy something because "it will do".
Save walking gear, fleeces, anoraks for outdoor activities like hiking/dog walking.
Make-up that suits you, lots of make-up tutorial videos on YouTube.
Plus confidence, attitude and a mirror.