Support

A common set up:
Flat armor marks
Flat armor seals
Scaling MR glyphs
Gold/time quintessences

I only play tanky supports like Taric and Leona and I set them up 0/16/14 (or whatever it is to get the two points in utility's gold/time)
as for build I grab an early philosopher stone and then rush Aegis of the Legion and then a frozen heart or shurelya's. I prefer taking on a much more tank oriented build than support so I end up with something like:

Shurelya's Reverie
Mercury's Treads
Randuin's Omen
Frozen Heart
Abyssal Scepter
Runic Bulwark

Quick edit: forgot to mention Ruby Sightstone. You know what it is and what it does, buy it, use it.

Yay . A support-to-be. Right. Let's get started. You may regret letting me get onto the topic of supports .

Rule 1 of being a support: Expect to get blamed for every of your adcs deaths. It's your fault you don't have 1 second cooldown heals shields speed ups and disengages. It's your fault you ran and didn't die when your adc was definitely dead. It's your fault you're "only" 0/3/20. The average person looks at the first two numbers and forgets there is a third. You do occasionally meet nice people, but prepare to get crap from people for no reason. It's your fault your team lost, and you're never the reason your team won. Yes, I hate people too.
Rule 2 of being a support: No autoattacking minions unless your partner is out of lane. One thing I'll agree on here. When playing ad carry and a support is autoattacking the minions, you feel like stabbing them if you're like me. So yeah, I'd avoid it. So don't play Taric :laugh.
Rule 3 of being a support: Try not to take kills. Because a) you'll get crap for it, and b) because kills are overrated anyway. However, if someone is being a total ass to you, I totally endorse taking every of their kills if you're in a normal match until they apologise.
Rule 4 of being a support: You are the only person on your team who should ever buy wards. I kid. But you probably will be the only one buying wards throughout the game. Sightstone is an item old schoolers like me dislike using, because I like almost too much vision on the map where possible, especially late game.
Rule 5 of being a support: Try to get items that benefit the team where possible. Sacrifice your own needs for others. That part can suck, but oh well.

Now that we're through a few golden 'rules', here we go. My masteries neglect those crappy consumables. My average masteries are as follows:

0/9/21 with Flash Exhaust/Clarity.

4 points in Durability, 3 points in Hardiness, 1 point in resistance, 1 point in Veteran's Scars, 1 point in Summoner's Insight, 3 points in Meditation, 1 point in Enhanced Recall (I don't care what anybody says, when supporting, seconds can count ), 3 points in Mastermind, 2 points in Artifacer, 4 points in Greed, 2 points in Wealth, 1 point in pickpocket, 3 points in Intelligence, 1 point in Nimble.

That is basically my average ranged support set (not that I have another one yet...) I do hold an unpopular opinion on Biscuiteer and ward thingy, but I think they're pretty useless, I've got my builds sorted around not using them. Anyway, to runes:

Armor Marks
GP10 Seals
CDR Glyphs
GP10 Quintessences

This maximises gold gain in all ways possible. Hence why I like it. You may find as a beginner to support Mana Regeneration seals as a comfort, although I do wish to stray you away from that trap. Once in it, it's hard to deal with less Mana Regen.

I generally split supports into 3 different categories (most supports overlap 2 or all 3 of these, but oh well, there are exceptions to each of these rulings...)

Utility Supports: Generally have a decent disengage, often a knock up. Also tend to play somewhat safe in lane. Some can survive a 1v5 because of their strength of disengage. Also tend to have a variety of spells, not based on sustain or ccing enemy with all 4 spells (usually a mixture of both). Major Examples: Janna, Lulu, Nami
Aggressive Supports: Generally have a grab, armada of stuns, and are generally somewhat tanky. Usually lack any sustain for their ally. Major Examples: Leona, Blitzcrank, Nunu
Sustain Supports: Generally are based around healing allies. Their kit usually lacks any or has very little QWE cc. Major Examples: Soraka, Sona, Karma (I'd love to put her in utility captain boo, but as she is, items give her cc .)

So where does Taric fit in here? He's an aggressive sustain support. Alistar is a real terror. He has a great engage, disengage and sustain. Nidalee? Same as Taric. Kayle? Aggressive Utility Support (I'm opinionated here). So yeah. If you've read up to here, then why??? You should be playing a support by now!

Edit: I just realised I spent half an hour typing that out on my phone. God, I wanted to be first to reply guys!
Edit 2: Argh, I forgot items in detail. But oh well. And BluAnimal has a fair point about tanky supports. You generally won't be needing as much of the utility tree as I use on ranged supports. Thresh is a bit of a pickle. captain boo may have some tips on building him specifically, because I couldn't get a good build going. If you want any help on Karma (), me and capt will a) love you long time and b) offer our two builds that focus on either: excelling her strengths, or covering her weaknesses.

A reminder to praise your supports for their good doings.

Karma excels against poke lanes. I forgot to mention that. Every time you see them about to poke, shield. If you miss a shield/their cooldowns are lower so you couldn't get your shield up again, you've got a heal (not massively powerful in lane, doesn't really scale up much in lane, hence why I max is second, but it's still somewhat decent). I've always thought Janna's laning to be somewhat decent. The jungler can gank all they like, it's rare that they're going to kill you or your adc with the strength of your disengage. I'd say Janna does have the worst laning phase however, purely because every other support seems to have a more powerful laning phase. I'd honestly say Soraka is easier than Sona in lane though. With Sona, you have risk factors when poking, with Soraka, you don't really poke a lot. Soraka teaches high level map vision (with her ult), Sona teaches balance of mana, poking and healing in lane. Saying that, they both bore me.

Zoning Janna means your adc is probably less efficient at last hitting than their one, because Janna performs better in an evenly pushed lane. Granted, zoning her is easy, but that just means less lane warding (although, warding dragon becomes a nightmare, you only have one safe route to it from blue team, and that's from behind, from purple team, you have a painfully lengthy route, but at least you get to properly ward dragon).

Karma is weird. She doesn't really excel at any point in the game, however, she has the single-handedly strongest heal in the late game. Her shield is very powerful with AP, however, lacks the bonus utility component Janna's and Lulu's shield. Her speed up and slow down is very handy, however, isn't hard cc. And the lack of ultimate component makes her late game medium. Strong heal, strong shield, and strong speed up/slow down is much better than Soraka's single-target heal aoe heal single-target silence and crappy 2 second poke. Karma's damage falls off no harder than any other support though.

Thanks guys!

What support would you say is the most basic? One that someone could, like, use to get used to the role.

quote Hmszelda

What support would you say is the most basic? One that someone could, like, use to get used to the role.

Soraka, Sona and Taric are quite often regarded as the basic supports. I'd recommend Nunu and Kayle soon after, because they introduce more aggressive lanes. Taric introduces aggressive lanes, but also has a passive that basically tells you to auto-attack minions, which is not a good way to start. Of course, when you're supporting without runes/masteries (at your lower level, you don't have the gold masteries yet right?) your ad carries are going to be...less amazing, and thus, you take a few cs to fund your build. Once you get runes and masteries, it's almost a crime to take a cs, because you're generating gold at a sexy pace :3. Oh, and farm the hell out of your lane when your adc backs. If they say "stop taking my cs", you tell them that they aren't gonna get there in time to get them. If they say "stop pushing the lane", you merely point out that you're last hitting the minions, and thus are pushing it no more than they should do.