German foreign policy under Bismarck had been dominated by the goal of preventing a coalition forming against Germany. To this extent Bismarck was successful keeping Russia on friendly terms with Germany, allying Austria and Italy, and keeping France relatively isolated. He put Germany forward as an international arbiter (such as the Berlin conference during the scramble for Africa and to prevent the complete destruction of the Ottoman Empire) and tried to keep Germany out of a situation in which it would occur the anger of the other great powers of Europe. However Bismarck's diplomacy had flaws, namely his alliance system helped drive Europe into the general state of mistrust that surrounded the build up to WWI. Furthermore Bismarck's "light handedness" in foreign affairs angered some more stringent nationalists who argued for things like preventative wars against Russia or further colonial ventures. By the end of Bismarck's reign, the cracks in his diplomacy system were showing which leads to the meat of the question.

This leads to the development of Welpolitik. The idea of propelling Germany into a world power. Bismarck's successors faced a tall order and often had to work under Bismarck's shadow (pretty much any serious action take with regards to German foreign policy was met with criticisms that "Bismarck could have done it better"). The new foreign ministers decided to simplify Bismarck's diplomatic system and remove the "juggling act" that Bismarck had engaged in. First to go was the treaty between Russia and Germany, since Germany felt an alliance between Germany and Russia would push Austria-Hungary and Italy away from Germany. Russia tried to get Berlin to renew the treaty, but German declined and Russia was driven into the arms of France.

The new priority for the post Bismarck foreign ministry was friendship with Britain, and they had some minor success in this regard with Germany and Britain settling long standing disputes over colonies in East Africa. However German colonial ambitions as well as their naval program greatly damaged relations and put to bed any chance of an Anglo-German alliance. Kaiser Wilhelm seemed to think the way to open up talks between the two was by "scaring" Britain by demonstrating German power, famous Kaiser Wilhelm had wanted to declare a protectorate over the Boer republics and send troops to help them fight Britain. He settled for sending a telegram congratulating the president of one of the Boer republics, an act that greatly damaged relations.

Further damage was done by appointment of Admiral Alfred Tirpitz as the head of the navy. Germany had been building a cruiser fleet to protect its trade and burgeoning colonial empire ( which angered Britain already) but Tirpitz decided to take a step farther and build a huge fleet of battleships. He was a follower of American naval strategist A. T. Mahan who had developed the doctrine that large battleships, were the essential prerequisite for the exercise of world power. This was a fatal catalyst in terms of Anglo-German relations.

The German's hands were kinda tied with regards to the navy because it proved so popular to Germans across the political spectrum and proved to be a uniting feature in an otherwise politically divided German landscape. The idea was to break Germany's naval dependence on Britain and force Britain to seek an alliance with Germany (or else risk conflict with a powerful naval force), of course this strategy left out the fact that Britain could seek alliances with other powers like Russia and France, or even newer powers like Japan and the USA.

So to answer the question of:

Was the German government simply unable to come up with a coherent foreign policy and blundered from crisis to crisis, or did they have some over arching strategy?

There over arching strategy was to force Britain into an alliance, since in Germany's mind British animosity towards France and Russia could never be overcome and Germany was Britain's natural ally. When Chancellor Bulow was confronted with the possibility of an Anglo-French/Anglo-Russian alliance he dismissed the claims, stating:

‘we can treat such matters with a dose of hair cream’

However, after the Entente Cordial which brought rapprochement between France and Britain, Germany switched its foreign policy into trying to realign the major power blocs. Kaiser Wilhelm tried to detach Russia by appealing to his Cousin Tsar Nicholas II, and did almost work but the Russian ministers choose France over Germany.

The next chancellor Bethmann-Hollweg made it his goal to reduce Anglo-German hostility, he succeeded by reducing Germany's naval commitment. Unfortunately any progress made in this regard was destroyed by the second Moroccan crisis. Basically Germany and France had agreed to cooperate economically in Morocco. But one German firm wasn't happy with the situation and started creating trouble with the aid German nationalist groups and colonial groups. France was meanwhile increasing its hold on Morocco for eventual annexation to France. Germany felt this was in breach of the agreement (it was) and so a crisis developed. One German state minster decided to use the opportunity to force a break up of the Entente by showing France that Britain would not come to its aid in the event of a conflict. Germany eventually sent a gunboat to Agadir, a Moroccan port. The crisis inflamed public opinion in Britain who felt Germany was being far too aggressive.

Eventually the crisis was resolved, with Germany gaining land in Central Africa and France gaining Morocco. But the fallout was huge for Germany. Anglo-French cooperation increased and German nationalists were greatly angered by the German government's failure in asserting Germany's rights in Morocco.

So to sum up, Germany pursued a policy of world power, and at first seemed rather blind to the consequences of their actions. They did eventually wise up to the situation and saw that the alliances were forming against them. But by then it was much too late to actually break the alliance system that had formed against Germany.