Most students end up looking to buy a drum kit and get confused when they see the vast range of drum stuff available and don't know where to start. I've written a rough guide that will hopefully help you separate the hype from the bare essentials and help you buy a drum kit that has a good overall sound but is adaptable enough to cater for you changing your opinion as you learn…
The main number you will come across is the diametre of the drum (22" for kick 14" snare etc.). The second number you are likely to come across is the depth of the drum; The deeper the drum the bigger the sound: A smaller depth usually gives a more focused, tight sound. The ply of the drums (6 ply, 7 ply, 8 ply etc.) is referring to the number of layers of wood the drum shell has. You won't have much control over this unless you spend a fortune on custom made drums but roughly speaking, more layers will give you a more focused, solid sound and less ply will give you a lighter, ambient sound.
There are a few different kick sizes commonly used, but the standard is 22" diametre. A 20" kick will give you more of a boom and less beef. I personally prefer a 22" because you can potentially get a much wider range of sounds out of it - a more "rock" kind of sound or, if tuned up a bit, a more jazzy thud similar to the 20". You can get bigger and smaller kicks but if a 22" is available go for one of this size. The kick I have is a 22" but is actually deeper than your average kick because I wanted a bigger, deeper sound that hits you in the chest.
14" is standard and anything above or below this usually has a fairly specific sound: a picolo snare for example will give you a really tight 'pangy' sound used a lot in jungle and drum and bass drumming, on the contrast, a 15" snare will give you a very deep sound. The depth of the snare also makes a difference, the standard sizing is around 6", so going for a 14" x 6" is a safe choice. Another element that makes a difference is the material the shell is made of: Aluminium gives you more of a pang, For example, Red Hot Chili Peppers' drummer Chad Smith uses a aluminium Pearl snare, on the other hand, wood gives you more body and solidarity of sound. Either material is suitable as the sound can be further manipulated with dampening the top head and careful tweaking of the snares underneath the drum.
12" (high), 13" (mid) and 16" (floor) toms are the standard for a rock setup. You can find anywhere between 8" and 18" really, but out of experience I would recommend the following sizes: 12" high tom, 14" mid tom and a 16" low/floor tom, although, any sizes around these will do the job. The depth of the drums makes a big difference with toms and I recommend 'jazz size' toms, which are slightly smaller in depth than 'rock size' toms, as they are a bit less unwieldy to tune and more pleasant and responsive to play.
Stands and Hardware
The stands you get should be 'double braced', which means they have two strips of metal side by side on the legs of the stand to make it a lot less flimsy. Good hardware makes a lot of difference to the playability of the kit and also how long it will last. A drum stool is also essential as using chairs can cause bad habits and difficulty playing if not at the optimal height for you. Your hardware is usually included with the drum kit. In summary, ensure you get a Hi Hat Stand, 2 Cymbal Booms, A snare stand, 2 or 3 tom mounts (depending on if your low/floor tom is rack mounted or free standing in which case you should have 3 floor tom 'legs') and a drum stool
Bass Drum Pedal
Beware of cheap pedals as they are horrible to use and often break quickly. Pearl make a good, basic pedal that isn't too expensive. This will make a lot of difference to the enjoyability of your playing: Cheap drum kits come with rubbish pedals and hardware so if you don't want to spend a lot of money you're gonna have to compromise. I won't go into anymore detail as the range of different types of pedal mechanisms and accessories available is staggering considering they all do pretty much the same thing.
The finish of the drums can make a difference to the sound: If you go for a laminate finish the resonance of the drums will be slightly dampened and can sound a bit choked, particularly the bass drum. A lacquered finish is better sound wise and looks nice but can be quite a bit more expensive. A natural/waxed finish is the other option and this is what I would recommend - I think they sound better and look more pleasant than the other types.
Drum skins make a huge difference to the sound of your drums: In terms of drum skin manufacturers, i usually choose Remo as their skins last, sound good and go for a fair price. Specifically, Clear Remo Emperors for the toms is what i would recommend, a coated Remo Ambassador or Powestroke P3 for the snare and a Remo Powerstroke 3 for the bass drum. I won't go into detail about this, but in my experience, this combination of skins will have a longer life whilst still maintaining their sound than other skins. Also, don't worry about the bottom heads - the ones that come with the kit will usually be fine.
The quality of the hi-hats and ride make less of a difference than the quality of the crash. I would recommend a Sabian Pro Pack as it's fairly inexpensive. I have used the ride and hi-hats from one of these packs for countless recording sessions and gigs in the past and they've always been fine. The Crash you get with this pack is OK but is a thousand times better than a lot of crappy cymbals out there that sound like you're hitting a dustbin lid such as some of the cheaper ones made by Pearl. So I would go for the Sabian Pro Pack, a bit more money than the cheaper packs, but in the long run they will save you having to spend another couple of hundred pounds replacing a bunch of not quite good enough cymbals. 14" hats are standard, 20" ride is standard and anything less than a 16" crash won't have much body to the sound and may crack quite easily, anything more than 18" will be too loud and big sounding for general use so go for a 16", 17" or 18" crash. You can get a whole variety of cymbals such the splash and china cymbals but my opinion on these is that they are special effects and shouldn't be used left right and centre.
A drum key or two is essential - make sure you get one with your kit. Drum keys are used to adjust various parts of your drumkit, most commonly, they are used to turn the tuning lugs on drums to control the sound. An 'O ring' can also be handy to help dampen the sound of your snare drum, but a similar affect can also be achieved using some tape and some tissue. A practice pad is a fantastic investment, especially if you are wary about buying a whole drumkit or don't want to make too much noise.
The most improtant thing to remember is that as with any instrument, there are no set rules, only guidelines. The best thing you can do is to invest time in experimenting with different sounds, techniques and products to discovery what you feel compliments your playing the best