To make a start you really need to know relatives who would have been recorded in the 1911 Census (the latest census currently available).
I have conducted many searches for living relatives.
I successfully found the next of kin for a WW1 medal found in a South Wales field. The return of the medal to the family in Tiverton was filmed for BBC Wales Today.
I have traced living relatives of over 100 officers and men from one WW1 unit.
I have assisted people who have posted on Social Media in the return to the correct family of books and bibles in their possession.