During the time of the coalition the Lib Dems reneged on many promises, including:
Tuition Fees
Nick Clegg campaigned on a promise to scrap tuition fees But once in government, Nick Clegg and his MPs voted to treble tuition fees to £9,000,
VAT
Nick Clegg campaigned against what he called a “TORY VAT BOMBSHELL” during the election. But it was a bombshell he helped the Tories drop - voting to increase VAT to 20%.
Tax Cut for Millionaires
Nick Clegg promised “fairer taxes in tough times”. Instead, he backed a Tory cut in the top rate of tax, giving 13,000 millionaires a tax cut worth an average £100,000.
NHS
Nick Clegg and his party backed David Cameron’s top-down NHS reorganisation from the start. It was passed thanks to Lib Dem votes.
Mansion Tax
In opposition, the Liberal Democrats said they backed a mansion tax. When given the chance to stand up for their own principles and vote for a mansion tax, they voted against it.
Sure Start
In May 2010, Nick Clegg promised to protect Sure Start and told voters that “.. Sure Start is one of the best things the last government has done and I want all these centres to stay open”. But in Government, the Lib Dems backed cuts to Sure Start - over 500 have been shut.
Police
Nick Clegg promised to put 3,000 more police on the beat. But in Government the Lib Dems backed Tory plans to cut more than 15,000 police officers.
Special Advisers
In opposition, the Lib Dems said that "special advisers should be funded by political parties”. During the coalition, Nick Clegg alone had sixteen Special Advisers - paid for by taxpayers.
Yes, it's it is easier to talk than to do but let's not forget that the Lib Dems were fairly ineffective while in coalition. And Nick Clegg, instead of insisting on holding to at least his main promises - say, tuition fees and VAT - settled for the AV referendum which was doomed from the start.