There are a number of official days when the Danish flag is hoisted, such as on the 16th of April for the birthday of Queen Margrethe II.
But also the flag is shown: On birthdays, at funerals, when picking up your loved ones from the airport, for school enrollment, at weddings, for divorce - actually there is no opportunity where you can not use the Danish flag. Most Danes see the flag as a garland or simply a beautiful ornament.
However, there are of course a few rules, such as the flag may not touch the ground when hoisting and a worn flag should be replaced immediately. You can not hoist any other flag besides the flags of the Nordic countries, the EU and the UN next to the Danish flag. Who wants to go into more detail here: There is a 64-page guide to the use of the flags in Denmark - the Danes love their flag.
So, if you're in Denmark, grab a flag and flag what it takes. Your Danish neighbors will be happy.