Brad writes a much longer answer (which I edited slightly in order to remove the lapdancers)
Waves: Ok, this subject is an interesting and challenging. There is a lot to deal with when you are fishing on the ocean, and waves are tough. Of course, the best thing that you can do with a wave is eliminate it. This is why fly fishermen are so fond of the flats. These areas are not very deep, and are fairly uniform in depth. To that end, waves crap out before they make it very far. The result is a calm area that is excellent for sight fishing and casting a fly.
Still there are others, like my fly fishing brethren on the east coast, that do not have the luxury of a good flat. So what are we to tell them to do? Several factors effect them. The first is wind from the incoming waves. There is a simple, yet rarely practiced, casting approach that will solve all of your problems. I am not going to get into the physics of this, but it does work. Here is the skinny. Make your cast so that you are shooting line just over the tops of the waves. As the waves come in, they create an area of low pressure above them. Simply, in the area just above the waves, there is less wind. Thus, you can shoot a fly over the top of a wave with relative ease. While this takes some practice to get good at, it is worth it.
Ok, now lets deal with the waves themselves. Ladies and gentlemen of the jury, I give you exhibit A. Please note the picture that Paul has chosen as the icon for the saltwater section. You will find it on page one of the site. You will note here that Paul is pounding through a wave with his rod in his hand. While I am sure that Paul did this only for effect (he is such a joker), I would point out that there is a better approach. What you may want to do is step back up on the beach. While I know wading is exciting, I will tell you that in heavy surf, you are beating the hell out of yourself for no good reason. Better to stand just beach side of where the waves are breaking. You can then make your cast beyond the breakers to where the fish are. This is easier on you. Also, the fish tend to hang out about thirty or forty feet beyond the breakers. For this reason, if you wade too far out you are going to be standing in the area you want to fish. Also, when you are standing in front of rolling surf, sight fishing is probably out. For that reason, you need to know where the fish "should be" and make your cast there. Naturally, if you notice things like a flock of birds thirty feet beyond the breakers... That would be an area you want to concentrate on. :-)
There are two other things that waves do to mess with us. Fortuitously, I have a solution for both of them. First, let's deal with stripping line. As you strip line in, you will find that the waves will carry it down the beach. This sucks for several reasons, but tangles are at the top of my list. What you need to invest in to correct this is a stripping basket. This little wonder fits around your waste for you to strip line into and shoot line out of. There are two styles on the market worth mentioning. The first is the plastic bucket model. This is a big plastic thing that you tie around your waste. I am not fond of these, as they are bulky and uncomfortable. The other style is the collapsible model. These are made of nylon material, with some metal rods that fold out to form the basket. This little wonder is fantastic. It is light, compact, and can be folded up when you need to move. Best of all it is half the price of the plastic bucket variety.
Now, let's deal with the other end of the line. Casting beyond the waves will cause some problems here. The surf will pull your line in for you, and that is not always a good thing. There are a couple of solutions to this one. Solution number one: Strip faster. As many of you know by now, I am a big believer in quicker stripping. Stripping line faster will solve the problem, as you will recover line faster than the waves are bringing it in. Solution number two: Cast on the diagonals. Rather than casting straight out into roaring surf, cast at a 45-degree angle to it. Believe it or not, the surf tends to mess with the line less this way.
Tides: I do not think that you can have a discussion about the ocean without considering tides. I think that tides are on of the most interesting things in the world. Just the fact that an object that is a few hundred thousand miles away can exert an invisible force that has enough strength to life billions of tons of water is pretty damned cool. What this accomplishes for the fly fishermen is even cooler.
Tides are the food delivery service of the flats, backcountry, and estuaries of the world. You can write an entire book on what the tides do and how they do it. I am not going to do so here, but if you have any additional questions on the matter I would be happy to go into greater detail. With respect to the estuaries that you are fishing, the tide brings in plankton. This is the building block of all life in the sea. As the tide comes in, the baitfish follow it. And, as you might guess, the game fish we are after follow the baitfish. Thus, when the water is up, the fish are there in greater concentrations than they are when the water is down. The rising tide also brings plankton to the crustaceans in the area that feed on it. Thus, crabs and shrimp are out in force and eating when the tide is higher. If you have a species like Kahawai that kind of likes shrimp and crabs on occasion, this can help you find the fish and then find the fly that will catch them.
Whenever I go for some fish in the salty water, I always check the tides. I would recommend that you hot a tackle shop and pick up a tide chart. In the absence of this you can go to any number of web sites out there for tide prediction. It does make a difference, so check it out.
Time: Due to the tides, and when they happen, you may find that it is beneficial to fish at some odd times. If high tide is at midnight, then you are wasting your time fishing at six in the morni... or at least on most days. Fishing at night requires nerves of steel for me. There is something kind of weird about wading out into the big black ocean at night. Personally, ever since I saw Jaws, I have been scared to death of it. So, I do most of my night fishing from shore or from a boat. The problem with darkness is that you can't see a damn thing. As a result, you need to know what is where before you toss out your first fly. To do this, you need to scout the area at low tide when you can see. You will want to make a note of any humps, rises, channels, and structure that you can identify. I use objects on the beach like palm trees, boat docks, and houses to triangulate the position of the structure. When you come back at night and the tide is high, you will have a hard time finding it by looking into the water. On the other hand, if you have a couple of points of reference on the beach, you will find it quickly. (Let's see. That hump was half way between the boat dock and the crooked palm tree on the left, and just over from that buoy.) It sounds like a weird system, but it works. It also keeps you from getting eaten by that bit Great White that is looking to munch on fishermen for dinner!
Let's talk Kahawai. These fish are predators that eat fish and lots of it. Whenever you see terns and gannets gathered, look below them for flashes. This indicates that the Kahawai are feeding below. The young Kahawai are often found inside estuaries that you are fishing where they are chasing anchovies. But they are normally more difficult to spot because of the murky waters. You will also find them in the coastal areas. They particularly like areas where rocks are present. They often follow the Trevally and generally feed on whatever they miss. So, if you throw to a school of Trevally and do not get a taker, you may get a Kahawai as a consolation prize.
These fish will generally take any small moving lure, but fly fishing for them is still in its infancy. I would concentrate on throwing smaller flies at them in the number two to number four size range. When these fish hit, they are not particularly aggressive. In fact, when compared to some of the more aggressive predators in the sea, they hit kind of soft. In comparison to the violent slash of a Barracuda, these fish will kind of gum the fly in a gentle gulp. If you do not see them eat the fly, you will feel a sudden gentle pressure that indicates that the fish is on. This is where the tranquility of the experience is over. Be warned that they will blow out of the water pretty quickly when they are hooked, and they run and jump like mad in an attempt to throw the hook out.
What to use: Perhaps the four favorite foods of the Kahawai are Anchovies, Mullet, Blue Pilchard, and shrimp. Imitations of these should be in your vest before you go out. Black and white and blue and white Clousers and Deceivers are mandatory equipment. I would also not go to the water without some flash flies and shrimp imitations. All of your flies should be fished quickly and in the most exciting presentation that you can muster.
Keep the lines tight and the reels screaming!