The Danes have some of the same advantages of Sweden, but also the unfortunate reality of a greedy and growing state to the South, initial economic conditions aren't great but a potential future union with Sweden could well allow the danes to shoot for Great Power status.
Maintaining good relations with Prussia will be hard but worthwhile in the long run, just as provoking them could be fatal. Denmark is unlikely to be able to afford colonial adventures.
In Vanilla, Denmark should start the game by laying claims around in Africa and Pacific. These claims will become extremely valuable to sell off to other claimholders in that state, giving Denmark some much needed money. Denmark should also start building good relations with Russia; the garant for Danish sovereignity. The last thing Denmark should start with is to declare war with Holstein right away. Prussia usually guarantees the independence of Holstein, so be swift in DoWing them, before Prussia gets its GI on them. Then annex Holstein when you can. This will give you 500.000 more pops to rule over. After building relations to 190+ with Russia, Denmark should try to go for an alliance with Russia. When the alliance is in house, Denmark should start land-trading Greenland, Iceland and Virgin Islands for non-cores of Russia. These will be a big boon to Danish economy, if you start converting people in the newly acquired states to craftsmen. This way they will immigrate to your capital state and your industry will get some much needed manpower.
When it is around 1845, Denmark should start converting its German pops in Holstein into soldiers and built up at least 20 cavalry divisions. Keep these cavalry divisions in stock and do not lay them down. When the year comes to 1846 set your military readiness to the highest, put down your cavalry in Holstein, your fleet in the sea so that Prussia cannot take Copenhagen and declare war on a German minor. This will trigger a set of alliances, where Prussia will get involved. Call upon your ally of Russia and let hell run loose. Start grabbing German minors and sattelite them. Annex Hamburg and Lubeck. Sattelite the rest. You should focus on Prussia early and knock them out of the war by taking their capital and some few provinces and then demand a peace, where they give war indemnities. This will allow you time to mob up the German minors, getting alot of prestige and satellites. After this war the rest should be a walk in the park.