Conservatives had been in power for 18 years, Major's government was divided over EU, and associated with sleaze and incompetence
Results
Labour won 418 seats with 43% of the vote
Conservatives won 165 seats with 30% of the vote (lost 178 seats)
Turnout was 71%
Governing Competence
Major was involved in several sleaze scandals the most notorious being with Edwina Currie (MP for South Derbyshire). There was also 'Black Wednesday" which resulted in rises in interest due to the ERM being dropped
Manifesto
Conservatives: control inflation, increase home ownership, improve Britain's defences
Labour: promised to cut NHS wait times and cut class sizes to 30 - used Pledge cards to show honesty
Leadership
Major was seen as incompetent and weak, as well as boring
Blair was seen as young, fresh and charismatic
Issue Voting
Mainly the fact that Major was associated with sleaze, division and corruption
Campaign
Major delivered a boring campaign with "New Labour New Danger"
Blair incorporated slogans, songs (Things can only get better) and adverts
Media
Labour managed to win the support of the sun (when they were already leading significantly) and were 20% ahead in option polls at the start of their campaign