I started mine when I was housebound last year. There are quite a lot of records on-line (some sites in a minute), but it's most important to ask all your iving relatives about anything they can remember, esp where people lived/died, what occupations they followed etc.
Be prepared to get totally absorbed in it (dh complained that I only ever talked about dead people!), and sometimes frustrated. To be honest I was obsessed for about 3 months, then it waned a bit cos I got stuck, then I found out something else and picked it up again, on and off all year. Last month I was contacted out of the blue by a distant cousin in Canada, who'd seen my tree on Genes Reunited.
try these as well as the ones already mentioned
free BMD index
ancestry website
british origins
1901 Census
Be prepared to spend a bit of money registering with some of the sites, and buying a few birth / marriage certificates.
Cat me if you need any more help, I'm fascinated by it, and would be happy to help if I can.
I'm planning to visit a few local history libraries and places to try to fill in some gaps in the next few months.