Be too high-profile and you risk straying into the line of fire if things go wrong, stay in the shadows and you face accusations of being a shrinking violet.
But two years after her husband Gordon Brown moved into Number Ten, Sarah Brown seems to have put her own gentle stamp on the job.
Whatever she does, whether it's tweeting about her charity initiatives, attending Glastonbury or representing Britain abroad, down-to-earth Mrs Brown seems at ease - and people love her for it.
Her night out on Thursday demonstrated her popularity. Despite being in a room full of supermodels at a soiree in London's Bond St, the 45-year-old was the centre of attention all evening, greeting fellow guests with her natural warmth and breezy friendliness.
The guest list at the Fashion's Night Out at Burberry event included Claudia Schiffer and Erin O' Connor.
Also heavily represented was the younger generation of glamour pusses such as Natalia Vodianova, Daisy Lowe and Alice Dellal.
Earlier on, mother of two Sarah was supporting Gordon and Tana Ramsay at a charity dinner held in his restaurant at Claridges.
There Sarah bumped into another Sarah – Duchess of York – whom she knows through their campaigning work with their mutual friend Naomi Campbell.