As you noticed, Destruction is pretty straightforward. Each cast and while continued casting, you will increase skill, but this has a caveat: only if you are attacking someone. If you're fizzling your spell in the middle of town, it's not going to increase it.
Alchemy is also straightforward: each potion created will increase your skill. As dpatchery notes, eating ingredients for effect determination will also increase your skill by a small amount.
With Enchanting, each enchant (or disenchant, as LessPop_MoreFizz notes) as will increase skill. dpatchery also notes that you can increase your skill by recharging items with soul gems.
Restoration, namely the healing spells, only increase skill if your health is below its maximum. The others only work if you're in combat or near hostile enemies: this includes spells like Steadfast Ward.
For summoning spells (essentially most things in the Conjuration school), you won't get a skill up for the summon until you enter the range of hostile mobs and, in the case of summoned creatures (like the Atronach and the Familiar), they do some damage. With bound weapons, entering range of hostile mobs is all that's necessary to gain Conjuration skill; however, using them in combat will increase their appropriate weapon skill, not Conjuration.
Alteration and Illusion spells that are targeted towards messing with hostile mobs need hostile mobs within range to skill up. Buffs, like Oakflesh, don't increase skill without hostility as well. Others, like Candlelight and Muffle, are recastable without hostility but only increase skill by a small amount.
According to the wiki yes, there is a way to tell by their names:
Red dragons: These dragons have appeared in Skyrim after the emergence of Alduin. Their bodies have a greyish tone with a light grey underbelly. Yol (fire) is their breath attack.
Green dragons: These Dragons have appeared in Skyrim after the emergence of Alduin. They have black skin with a distinct green glow. Commonly found in forested areas, they can use the Raan Shout (animal alligiance) to call nearby animals to their aid.
Frost dragons: Frost dragons appear in Skyrim after the emergence of Alduin. Frost dragons are white with massive protruding black spikes coming out of their back. They predominatly use Fo (frost) breath that deals damage, slows the player down, and reduces stamina.
Blood dragons: Blood dragons appear in Skyrim after the emergence of Alduin. They are recognized by their green-grey, crowned head, and large fan formation on the end of their tail. They become common at level 15-16, and use Yol (fire) and Fo (frost) breath attacks.
Elder dragons: Elder dragons appear in Skyrim after the emergence of Alduin. Orangeish in color can use either Yol (fire) or Fo (frost). These attacks are generally strong and debilitating. Their tails can rend a forcefull hit and have the spade shape at the tip.
Ancient dragons: Ancient dragons appear in Skyrim after the emergence of Alduin. These dragons have a tremendous amount of health and can use either Yol (fire) or Fo (frost) as the Elder Dragons do. Just as Elder Dragons they have a spade shaped tail tip.
- Skeleton dragons: Skeleton dragons appear in Skyrim. They are usually in dungeons, caves, and any underground structure with draconic lore. Although flightless, they are still dangerous. One such dragon appears inside Labyrinthian. These dragons don't have dragon souls.
Dragons that use fire based attacks are 50% more resistant to fire based attacks although 25% weaker when faced with frost based attacks. Vice-versa for frost breathing dragons
Using those clues, you can try to discern what type they are before you are fully engaged but most dragons seem to be of either type, so there's no easy way to tell unless you spot them fighting something else.
Best Answer
The only way you can tell if you gained any xp is first to find out how much skill usage (i.e. xp) it takes you to get to the next level of sneak.
You can do this via trial and error using the command (save first):
Once you figure out the exact number (lets say its X), you can then reload your save and proceed with your experiment. If you have gained experience, then the command:
should bump you to the next level. If not, then you haven't gained any xp.