The next step is complicated and tedious. First, grab some milk, a fish, and a few bombs. Go down the well in Ikana, near the house where you fight the Poe Sisters. Put on the Gibdo Mask and talk to the Gibdos,which want items in return for passage to the next room. Most of the items I didn't mention can be found in the well or around Ikana. this well is very labyrinthine, but you will want to remember the gibdo that asks for a big ghost. at some point you will find a big poe. defeat it and catch its spirit in a bottle. give it to said gibdo, and you should be close to getting a mirror shield and passage to Ikana Castle. You should know, if you haven't found out, that there is a secret entrance to Ikana Castle near the sign that says "Impenetrable Ikana Castle" or whatev. It is a hole in the wall. You can only get thru this entrance if you have the mirror shield. You are probably short on time so reset it. Now get a powder keg and go back to Ikana Castle. All I can really tell you is that you need a powder keg for Ikana Castle (not to get thru the front gate, but for later) and that the ReDeads within will not be hostile and instead do a dance if you put on the Garo Mask. Oh, and you will want to burn the curtains in the miniboss at the end with a fire arrow, and point your mirror shield on the Stalfos Guards and King when they're ko'd. Once you beat this miniboss, you will learn the Elegy of Emptiness, which lets you make copies of your 4 forms. Now, on the way to Stone Tower Temple, there is only one more thing: when you see the owl, you must hold down the 3 nearby switches in the order middle-left-right.
Good luck.