How To Start a Family Tree
1. Start With You
It may seem obvious but start with yourself and work backwards. Add all the people you know are related to you and as much information as you can. Heard the one where all English people are related to Shakespeare? If you are related to him then there are approximately fifteen generations between you both and a total of 32,7681 direct ancestors of which he is one, that's a lot of people to trace to get to you.
2. Interview Your Family
Once you have put down everything you know ask your family what they know. Who their parents were, grandparents. Where they lived, are there any family stories? There are a list of questions on 18 Questions To Ask Your Grandparents Before It's Too Late that will get you started. Don't push too hard though, remember that what is socially acceptable now (for example illegitimacy) wasn't only 40 years ago. If they don't want to talk about something that's fine. A little information is better than none.
3. Record Everything
Write it all down. No you will not remember who, when, where or why! There are lots of websites where you can record your family tree, many of them free but don't rely on one place. Keep a record on your own computer and on paper too.
4. Read And Obey The Golden Rules
These aren't just my golden rules they are rules that all serious researchers use, I have just put them in one place for you. Everyone will ignore at least one of these and eventually have to go back over all their research and correct it. I made mistakes, you will too but read these and do your best to stick to them.
5. Gather Any Documents You Already Have
If you are lucky enough to have a family bible with names and dates of birth in it then record the information. Ask your family if there is one, who has it? What is written in it? Ask family what birth certificates, marriage certificates and death certificates they have and take copies. Newspaper cuttings? School certificates? Anything they have may prove to be useful.
Each generation doubles number of direct ancestors so 2 Parents, 4 Grandparents, 8 GGrandparents, 16 GGGrandparents and so on. When you get to 15 generations you have 32,768 direct ancestors.