You could get away without using your navies as the CP because you fought a continental war against continental enemies. You even managed to keep Britain neutral in your last game and so perhaps could have been a bit more aggressive with the HSF, perhaps raiding the French Channel coast to whittle away at their NW. Likewise in the Baltic and Black Seas.
Like other aspects of WW1G, the naval war is chock full of historical flavour and once you get past the built in bias' against the Royal Navy in the Stock game, many of the aspects of the real naval war shine through. That's why I wrote my Naval Mods, the historical foundation of the game's naval sub-game is solid enough that modding out the uber-High Seas Fleet seemed worth while.
Essentially, you use navies in the game as they were used in the event. As the CP, not using your fleets in most situations is probably the correct answer to the question How do you use your navies? For the Entente the answer may be different particularly if Britain is at war.
Amphibious operations are eased by gaining sea control, an expensive operation that is not guaranteed. Stock requires six-ship units (mistakenly called 'ships') to attempt a control mission but I edited it to three. This seems to do a couple of things, it makes naval actions in the Black and Baltic Seas a practical proposition, it means that on occasion the German's have the option to combine raiders and attempt sea control in the far seas and it makes the smaller fleets like the Greek and Dutch navies relevant.
Just open the file NavalMissions.csv, find the line:
and change it to:
Now it only takes 3-ship units to attempt sea control and you may find that, in the long run the naval AI will be more active, particularly outside the North Sea.
As the Entente you absolutely need Britain in the war and you need the Blockade. You also need to build all the destroyers you can and send them out into the North Sea and North Atlantic Ocean to fight the U-Boats. I have found that if you dominate these areas the German AI will often not pour a lot of resources into building U-Boats. However, if it does, the British economy and NW can be hit very hard, particularly starting from the winter 1916-17 interphase in my experience. Provided of course that the CP can hang on that long but if the CP gets the upper hand in the U-Boat war, your pretty battleships become more or less useless.
The HSF may contest command of the North Sea, if it wins, the effects of the blockade are nil until the next Interphase but since your anti U-Boat forces are light cruisers and destroyers, these may be vulnerable to attacks by AI heavy units. Against this is the fact that using ships aggressively is expensive in money and losing them costs NW. Building additional capital ships is an expensive long-term investment and often by the time you have enough money to spare, you are running out of time. Besides, you may not need them since you get a free fleet if you can bring the USA into the war.
Build and deploy mines every Interphase that you can. Plant them off the German naval bases and in British coastal waters; mines can achieve some spectacular naval attrition at little cost. Keep your battle fleets on patrol missions ready to support your light forces. Because the German raiders are so difficult to kill, keeping squadrons overseas will probably last for years. If Japan joins the Entente, the Japanese fleet can be useful for raider hunting in the far seas. If Italy is an ally, there is little for that fleet or the French Navy to do in the Med. This is as it should be but if Italy joins the CP, the French Navy can have a meaningful role conducting raids and the like. The Adriatic generally fills up with mines and can be expensive to enter so leave it as an Austrian lake.
I think most of the above is applicable whether you're running the game modified or stock, the naval engine is, in my opinion, pretty representative of the real situation.
Personally I think the game is at its best in the 1915 or 1916 Campaign scenarios rather than the Grand Campaigns. With these you walk into somebody else's mess and are expected to fix it.