It's essentially maintaining good hygiene techniques from simple things like taking a bath daily, brushing, wearing clean clothes, smelling nice amongst other things, it's important to maintain an all time decent appearance.
Asides from the fact that good grooming knocks years off one's actual age it's best to always present one's best self at every point in time and at the very least not to offend people with one's hygienic presentation (or for some people the lack of it).
1. Neat appearance
A well put together appearance is a must. Clean clothes, moderate makeup and tamed body parts as well as nice scent should form the basis of everyday appearance. One doesn't have to wear the most expensive piece of clothing to look neat or good.
Wash clothes clean/wear clean undergarments etc and smell nice.
2. Remove unwanted/unsightly hair
Unsightly hair should be tamed or shaved. Facial hair/moustache (hairy lips on ladies), hairy legs, hairy armpits etc should be shaved/waxed clean. 'Unibrows' are no no they should be neatly trimmed and separated for a clean/no fuss appearance.
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3. Keep hair tamed
Hair in any style should be kept tamed; packed neatly (if need be) trimmed where necessary and shampooed and treated as they are one of the first things people notice on others. Hair with major dandruff and dry scalp should be carefully treated and tamed.
4. Be appropriately dressed
There's always a theme for every occasion and that should form the basic get up. Going to work in an outfit for a cocktail event for instance will definitely look out of place just the same way going to a club in a pant suit will look super ackward.
As much as possible dress appropriately.
5. Smell nice
Smell good everytime, invest in deodorant/ antiperspirant sprays, perfumes/colognes and so on especially if liable to sweat a lot.
Body odour, sweat/stale smells should be avoided at all cost. Maintaining a general sense of good hygiene will also ensure you stay smelling fresh everytime and this goes a long way to make a lasting impression.
6. Maintain great oral hygiene
Great sense of oral hygiene is necessary. No one wants to open their mouth to talk and everyone gives an excuse to leave the room or move away as far as possible.
Great dental hygiene starts with brushing daily, using mouthwash/rinses while using breath fresher, mints etc comes in handy during the day to refresh.