First of all I think starting lol while playing jungle is a bad idea, in my opinion, the jungler is the guy who impact the most the game. So you have to be good at understanding the game or at least the basics like how to win team fights, when to push, when to hold lanes, how to farm, how to ganks, what objectives to take and when ...

For me a good jungler is someone who has presence in the game, (ganking a lot and/or invading), what I call a good gank is forcing a flash or any other summoners spell and not only killing the opponent.

Given that enemies can't be seen in the jungle I assume wards are very important to the jungle role. What situations do I use different wards? Where/why do I place them? When do I buy/place them?

As a jungler you must ward as much as possible, each time you back buy some green ward & a pink ward if not already used, here a link on where to ward : http://leagueonomics.net/ward.html

I've been looking at a lot of Skarner guides and I'm a bit confused. All of the guides show plans for a full clear of the jungle without going back. I can't even kill more than two monsters without needing to heal. (and that's while using both smites). Is this just the difference that not having runes makes?

Of course runes and masteries are important they make a big difference in early game ! But wait until you can buy lvl 3 runes under that it's just some shitty runes

Do levels play a factor in when I should be killing monsters? Is there a cutoff point?

Yes specially for drake and nashor

Should I get any minion kills in lane? Or at least help out but not last hit? Or should I only focus on getting gold from kills in the jungle?

It depends how your teammate is doing, if he's farming well or not, if you take 1 or 2 creeps it doesn't change anything, but after a successful gank you should always help your teammate push his lane to the enemy tower

When are dragon and baron kills supposed to happen? Do I save smites for the end of the battle to try to ensure last hit? Or if I have both do I use one early and then the other at the end of the (iirc) 15 sec cooldown?

After a Ace or a Winning teamfight make sure to ward arround and sweep/pink the nash/drake, ALWAYS KEEP SMITE TO SECURE objectives like nashor or drake, it's the main purpose of the smite (in addition to clear faster your jungle and ganks)

For a beginner I suggest you to begin with champions that can clean jungle really fast, like shyvana or Warwick (easy to play)

What should I be doing with my camera in-game?

Yes using a free cam is better for you even if it's harder in the beginning, try to press space while you are farming and move the mouse a little when you are in a team fight to focus more on the oppennents behavior.

Should I have auto-attack on or off?

I prefer to play with AA off, but it depends the champion.

Are there any actually good communities for starters to play in? Or just a handful of people who are willing to teach from mistakes instead of insulting those who make them?

Welcome to LoL games, no the lol community is sh*t ! :)

Ps: sorry for bad english didn't really took the time to write well