The Scottish Executive initiative was launched on Monday by Health Minister Malcolm Chisholm.
Its target is to increase the uptake of the jab to 70% - a level attained in only two health board areas last year.
The £1.5m advertising campaign will include billboard posters in inner city areas where uptake was low last year.
There will also be press and television adverts, combined with efforts to get the message across in GP surgeries across Scotland.
Letters will also be sent to all those eligible for immunisation on age grounds.
The Don't Let Flu Strike campaign is targeted at an estimated 800,000 people who are aged 65 or over, or who have long-term medical complaints.
They are being urged to go forward for the free jab, which protects those most vulnerable against the complications of flu.
Target met
Last year the Scottish Executive set a target of 65% uptake of the injection.
This was met or surpassed in 11 of the country's 17 health board areas, with Dumfries and Galloway and the Borders achieving more than 70%.
The poorest response was in the Western Isles, where only 50.6% of those eligible received the jab.
Mr Chisholm issued a warning against complacency as he launched the campaign on Monday.
He said: "After two winters of relatively low levels of flu, people need to be aware that previous years' immunisations will not protect them against this year's strain of flu.
"To achieve protection this year, it is vital for everyone in the targeted groups to come forward for a free flu jab this year.
"Around 800,000 Scots aged 65 and over and those with longer term medical complaints such as diabetes, asthma and kidney disease are being targeted through this year's campaign."
The £12m cost of the campaign includes £4.6m on vaccines and payments to GPs of £5.6m.
Essential protection
James Kennedy, the secretary of the Royal College of Nursing Scotland, welcomed this year's initiative.
"Flu injections offer essential protection from sufferers of illnesses such as asthma and diabetes, as well as older people," he said.
Age Concern director Maureen O'Neill added: "Age Concern supports the provision of flu jabs and particularly for those who are frail, and encourages them to attend their GP practice as soon as possible."