by writing down a list of all your living relatives and deciding who is related to who and in what way. Then think about all the weddings and funerals yoiu went to and try to find old photos and identify everyone related to you. Then start talking to your living relatives, especially the older generation, and find out what they recall of their parents and grandparents. it can be very interesting. Once you have done some of this, decide which side of the family you are going to look at first, choose one that is close to where you live now if possible, as alot of the research wil be easier and you will learn about the sources available easier.
Try to find out if any of your family, including any members living abroard, have already begun the research, this can sometimes be the case and so you can exchange and not duplicate reseach.
Find out what your local library has available for general reseach and also practise usinmg some of the online national indexes on Ancestry.co.uk. Look for your own birth first to work out how the indexes for Births Deaths and marriages in England and Wales work.