Radak: The matter is repeated in different words. Lamedeni is to teach me until I will know. "Derachecha Hashem Hodi'eni" is like Moshe said "Hodi'eni Na Es Derachecha v'Eda'acha" (Shemos 33:13). When he will know His ways, he will know Him. I.e. when He will make him understand all the creations - their nature and their ties to each other, and he will know His conduct with them - of the Klal and the individuals.

Malbim: This refers to needs of the Nefesh. Derech is a great fixed path for the Rabim. Orchos are branches from the great path to the sides. For the great path, Hoda'ah (informing) suffices. For the particular branches. Limud is required, for there are many and they are not so recognized. In the Nimshal, Derachecha Hodi'eni are the general ways in which You conduct Your world, e.g. mercy, grace, slow to anger and great Chesed. Inform me, so I will conduct in those ways. "Orchosecha Lamedeni" are the details that separate from the great path, that Hashem conducts at particular times and places with individuals. Similarly, one must know how to conduct in particular times and matters that depart from the general way, e.g. to be cruel to Resha'im and to be haughty and brazen against them. One must learn this!