Shooting From Cover
One of the tricks of the trade in Dead Rising to take advantage of, especially in boss fights, is the way that you can sometimes attack slow-moving or stationary targets without exposing yourself to fire at all. To do so, take stock of the fact that Frank, while in aiming mode for a ranged weapon, tends to lean a bit to the right. If you position yourself behind a pillar or wall and aim around the right corner, you can often find yourself hitting your targets without them reacting to your presence or counter-attacking. Just be sure that the shots are actually hitting your target; if you stand too far away from the edge of your cover, you can fire your bullets directly into it without really being aware of it. If you shoot a wall or something similar, sometimes your bullets will just disappear. Look for blood to come out from your target to ensure that you're actually hitting them.
In most boss fights, your targets will be too mobile for you to take advantage of this technique, but if used at appropriate times, it can be quite helpful to your overall prospects for survival.
You're going to have a cornucopia of weapons to select from in Dead Rising, with the claimed number being around 250 individual types of items that can be used against zombies in some way. Many of these are simply going to be poor choices for an aggressive action, however, as they'll either be too weak or too difficult to use properly. Sure, you can try whacking on a zombie with a toy sword if you like, but you'll have to hit them a hell of a lot of times in order to kill them. The opposite problem is apparent when you use weapons like cash registers, benches, or TVs. They'll kill what you aim at, but they're so slow that you'll often be moved out of position by your attacks, allowing zombies to attack you from behind.
There are a few standard weapons that you can expect to be using quite a bit, though. This section is intended to give you an idea of what to look out for.
Lead Pipe: A solid weapon in the early game, and whenever you have to make your way past a large number of individual zombies. One can be found in the Warehouse, on the floor. When swung, will usually instantly kill any daytime zombie, and can be swung quite fast, to boot. The speed of the swing makes this useful when dealing with many bosses, since you can bust it out quickly to stagger the boss and stop their movement temporarily.
Baseball Bat: Another good choice for melee combat. It has a longer swing than the Lead Pipe, and doesn't have quite as much range, but will swing through multiple enemies, knocking them down and away from Frank. When you have to get through a dense crowd of zombies and don't have a shotgun at hand, then spamming out bat swings will usually get the job done quite well.
Katana: An excellent weapon, although it will tend to break rather quickly. You can find one of these early on by jumping off the railing in the Colombian Roastmasters store in Paradise Plaza onto the awning below. Quick swings, instantly kills zombies, can usually kill multiple zombies if they're bunched up. A slight amount of recovery after the second swing, but not nearly as bad in that regard as the Battle Axe or the Sword.
Nightstick: One of the best crowd-control melee weapons, perfect for wading through zombie hordes. Nightsticks are dropped from zombie cops that carry them. There's virtually no downtime with this weapon, no recovery from your swings, allowing you to simply jam on the attack button and use it to knock down any zombies in your path. If it doesn't kill a zombie on the first swing (and it usually won't, especially at night), they'll usually keep standing until you kill them, preventing any awkward "I thought that guy was dead!" moments.
Hunting Knives/Cleavers: Plenty of the zombies in the mall are apparently freshly returned from safari. These guys wear little Hawaiian shirts and will attempt to slash you with their knives if you get too close, but like most other weapon-wielding zombies, they'll drop the knives the first time they take damage. Hunting knives and cleavers are great for quickly slicing through zombies. Since they can be swung quickly and recover almost instantly, you can simply spam the attack button and be almost sure of getting through a crowd without a scratch. Since they do attack quickly, though, you'll often go from having a fresh weapon to a broken one in the matter of a couple groups of zombies.
Handgun: The handgun is one of the most common ranged weapons in the game, and is going to be found on many of the zombie cops stalking the mall's hallways. As a single-shot weapon, it'll be useful for getting headshots on zombies in your path, but you'll have to use the aiming mode to get the most use out of it; shooting without going into aiming mode generally will only wound a zombie in front of you. Thus, it's not quite as useful as a shotgun or an SMG, but it'll still be handy in the early portions of the game or against certain bosses.
Handguns are probably better for survivors than any melee weapon, but they're still likely to be the worst ranged weapon choice for survivors. If you have no other ranged weapons to hand over, then sure, kill a zombie cop and give them a handgun, but don't expect them to be particularly handy with it.
Shotgun: A fine weapon, if you can find them. There are no fewer than three shotguns in the Huntin' Shack in North Plaza, but they're scarce besides that. Still, if you can grab a shotgun, you'll find that it's going to be one of the finest zombie-killing weapons in the game. The spread of the weapon is such that you can fire it from the hip - i.e. without going into aiming mode - and still be relatively sure of hitting anything in front of you. When firing into especially dense crowds of zombies, a single shotgun blast can often kill four or five zombies in a row. Shotguns are especially handy in most boss fights, as they can be fired either in aimed mode or in freeshooting mode, and still have a good chance of hitting the boss either way.
Submachinegun: SMG for short. You can find SMGs above the camera shop in Paradise Plaza (walk along the blue awning to reach it) and in the fountain in Al Fresca Plaza. These are the only fully automatic weapons you're going to have for the bulk of the game. They're not terrifically useful against zombies, since you'll usually have to go into aimed mode to nab headshots, but if you do use aiming mode, then you can quickly take out a horde of zombies by aiming at the average level of their heads and sweeping back and forth while holding down the fire button.
SMGs are also great to have in hand for boss fights, as you don't have to be as accurate as you would be with a handgun. They're also a good second choice for giving to survivors (after shotguns), since they'll generally be able to mow down multiple zombies more rapidly than they would with a handgun.
Sniper Rifle: Sniper rifles are typically only going to be used when fighting against psychopath opponents and other bosses. They'll kill zombies in one headshot, obviously, but they're overkill against zombies and will slow you down as you zoom in and line up your shot; better just to jumpkick them aside. Even against bosses, they're typically not going to be very useful, as most bosses will have ranged attacks that will make you pay for standing still too long, which is required if you're going to take careful aim with a rifle. Rifles can be fired without going into aimed mode, but there's not much point in doing so, as they act just like handguns in that instance.
We haven't run across any survivors that can actually use sniper rifles. There may be one or two that can handle them, but we didn't carry the weapons around often enough to get a very large sampling.
Machinegun: Later in the game you'll start running across machineguns. These guys are vicious and powerful, and are capable of laying waste to even the most powerful of opponents, and by the time you actually start getting them, you'll need the firepower they represent.
Maintenance Tunnel Keys
One of the quickest ways to get from plaza to plaza in the mall is to take the shortcuts through the Maintenance Tunnels. To obtain the key for all of the different locked doors there, head to Leisure Park, grab one of the cars in the parking lot there, then head down into the tunnels below the mall. If you check your map, you'll notice that there's a single dead end in the center of the tunnels. Head there and enter the door nearby to find a small storage space. The Maintenance Tunnel Key is inside this room. Obtaining it will let you access the tunnels from many of the plazas themselves, although you may not always find a vehicle when you reach them.