Through a massive naval build-up.

Alfred von Tirpitz was the architect and chief promoter of a new German Imperial Navy, and it was his First (1898) and Second (1900) Fleet Acts that seriously frightened the British Empire (which of course enjoyed the most powerful navy at the time.)

The Second Fleet Act planned for some 36 battleships and 11 cruisers by 1917. For comparison, the British Empire's Grand Fleet had about 40 battleships (and countless other kinds of ships, but the battleships proved to be more attention-grabbing since the Dreadnought was launched in 1906) for 1914. The High Seas Fleet's build-up was interrupted by World War 1, but you can probably imagine how alarming the british would find a huge german fleet being constructed in the North Sea. After all, the North Sea was specifically the point Britain hoped to easily blockade for any eventual war: that was a huge strategic advantage over Germany the British had. Furthermore, it's probably worth mentioning the Tsushima battle (1905) between imperial Russia and Imperial Japan, and furthermore the crushing of the Spanish Armada in 1588. Imperial Russia lost just one strategic battle to an up-and-comer using state-of-the-art battleships and would never rebuild that fleet (as an Empire at least). The Brits themselves completely crippled the Spanish for good by destroying the Armada: it's not easy to rebuild ships. One loss, and you're basically done.

So, a naval focus would be the best bet to unseat Britain, who relied on its preeminent navy to bring in resources, protect trade, and blockade enemies. Germany already had a supreme land force---the creation of a navy would completely unsettle what advantage the British had left.

Sources: The First World War, by John Keegan. Tirpitz, Architect of the German High Seas Fleet.