When researching individuals from the UK it may be beneficial to know the identity of close family members, which can be achieved by using sites such as Find My Past.
Using David Cameron, a previous UK Prime Minister as an example, first get a few basic details for the subject. On Companies House he is listed as David William Donald Cameron, with a date of birth in October 1966. Then, first of all searching for the record of his birth, will provide details of their Mothers Maiden / Last Name and the exact area they were born in. Remember that when you have a baby you have several weeks to register the birth, so babies born towards the end of a year may not actually have their birth registered until the start of the following year.
Next, now that David Cameron's Mothers Maiden / Last Name is known, a search can be made for any possible Siblings. If the Surname & Mothers Maiden / Last Name you are researching are fairly common you may want to change the date range to 10years or even 5years either side of your subject's year of birth, and adjust the location to closer to where your subject was born.
Then you could search for the Marriage of David Cameron's Parents, using the Surname & Mothers Maiden / Last Name. Again if the names you are searching are fairly common you may want to adjust the date range & / or location of the Marriage. Obviously, people don't have to get Married but always use your own life experiences when you conduct your research.
Then you could search for any Marriage of David Cameron. Again if the names you are searching are fairly common you may want to adjust the date range & / or location of the Marriage.
Then you could search for any Children born with the same Surname and with the same Mothers Maiden / Last Name as on the previous Marriage record. Again if the names you are searching are fairly common you may want to adjust the date range & / or location of the Marriage.
It is worth bearing in mind that the Official Birth & Marriage records held by Find My Past only go up to 2005 for Marriages and 2006 for Births. Other sites, such as Ancestry & Genes Reunited, have areas where family trees can be uploaded by account holders and often accessed by others, and these may contain additional useful information and documentation.