Ok, so I finally have a short handle on soul gems. (I use soul trap and then I kill them to fill one.)
So far it only works with wolves and other low level creatures. It fills a soul gem. A petty one.
It takes A LOT of petty soul gems to fill up my depleted enchanted weapons.
When I kill a bandit it says there soul is too big for the gem.

Can someone give me a run down on what fills petty, lesser, common, etc?
Also, if there is an easier way than using soul trap?

Thank you all and may Talos bless you!

The higher level the creature the higher level the soul gem you need to trap it.

NPCs got black souls. Only Black Soul Gems can hold them, and they are all Grand.

I second this, so if anyone has answers and I am sure there are more like us out here that could use some help. As far as how to catch their souls, you will come across weapons that will capture their souls if killed within 'x' amount of seconds. I use a bow (am a stealth and bow build) and every time I hit something it dies instantly and their souls are captured.

This, just this and nothing but this.(Not really) But seriously, this is all you will need.

Ok, maybe I'm not being clear. I'm a noob. I need a break down on each soul gem and the soul to fill it. Anyone know?

Id like to know if the oblivion system is still in place. If I soul trap a mudcrab and I only have a grand gem does it get filled with a petty? If later I trap a dragon does the same gem become refilled with a grand soul?

Well, soul gems can only capture souls of a particular size. I've not indulged in Skyrim as yet, but what little I have, it's pretty much the same as Oblivion.

e.g.

You kill something that's got soul trap active on it and you'll get:

Petty soul - like rats
Lesser souls - like mudcrubs
Common souls - like wolves I would imagine
Greater souls - bigger monsters, perhaps Dreugrs?
Grand souls - like mammoths and boss monsters
Black souls - humans

However, bear in mind that if you're carrying a Grand soul gem only, and kill a rat, then you'll have a Grand soul gem filled with a petty soul. But if you're carrying smaller soul gems, then the soul with go into the smaller more appropriate one by default.

You can only put human souls in black soul gems too - nowhere else. I'm not sure if black souls gems accommodate creatures other than humans though; I wouldn't have thought so.

Petty soul gem can hold creature souls below lvl 4
Lesser soul gem can hold creature souls below lvl 16
Common soul gem can hold creature souls below lvl 28
Greater soul gem can hold creature souls below lvl 38
Grand soul gem can hold any creature soul
Black soul gem can hold any human soul
Soul Gem Fragment cannot hold any souls

It sounds like you want a breakdown chart of each creature's soul size/power. That's in the official guide books. Someone will probably post it online (UESP wiki and elsewhere, I would imagine).

However, using such guides can make the game very boring and certainly is not role playing.

I would vote for Beth adding some reference books in the game world, though, so that characters can research some of the information about soul power.

They're not supposed to, but as a result of a bug the ... special ... black soul gem actually does. The description and dialogue says that it cannot hold 'white' souls, but it can and does.

http://elderscrolls.wikia.com/wiki/Soul_Gem_%28Skyrim%29 with notes on where to find them

If your black soul gem gets filled with something less than grand, which can happen, just drop it and pick it back up. Dropping soul gems releases the soul and keeps the gem intact for another soul.

Also as another poster already mentioned, get the Black Star from the Azura Shrine quest. That's all your going to need once you got it.

that... depends on which route you take... then it can either trap white soul or black soul.

http://www.uesp.net/wiki/Skyrim:Souls

Oh wait, am I to understand that using a soul gem breaks it? Oof

That never happened in Oblivion, the grand soul gem remained filled with a petty soul.
It still does that.
A soul will go into the lowest container available.
Only black soul gems can hold the souls of any of the playable races.
Most of the rest of the creatures are up to common, there really arent that many grand souls either, usually the undead boss at the end of a dungeon.
And mammoths have grand souls, I think.

Here http://www.uesp.net/wiki/Skyrim:Souls

And like someone pointed out you should know what souls you are trying to get and make sure you have appropriate gems in your inventory. It svcks to waist a grand soul gem on a petty soul. Thats 1500 gold waisted. Humans and vampires are all grand souls but they are black souls so you need black soul gems to trap them. Black soul gems are very rare but there is an alternative that i wont go into because it's a spoiler, i know of one vendor who has chance of selling them too.. But yeah trapping human souls is considered EVIL. Don't really know why it's "ok" to trap other creatures souls, but yeah i wouldn't want to be stuck in a necklace or sword...

I like that idea!

okay let me explain

skeever, wolf, dog - petty

draugr, skeleton, undead in general, some type of animals - lesser

ice type animals (ice wolf, ice saber cat, polar bear), spriggan, trolls, a bit harder type of draugr, and lots of type of creature - common

giants, mammoth, draugr lords and boss, anything that hard to defeat until you're around 35 - greater

human NPC - grand (only black gem could captured human souls)

I have azura's star but it never gets filled matter what soul I trap! Do I have to equip it or something for it to work? Any help here would be awesome!

Oh didn't know this. This is a nice workaround until they make a mod that prevents those petty souls from getting in my grand gems.

http://www.uesp.net/wiki/Skyrim:Soul_Gem

This should be helpful to you.

Also, this statement in the Wiki:
Soul Gems are consumed upon being used to recharge a weapon. This is one reason why it is a good idea to fill your Soul Gems as much as possible (ie. Grand Gems for Grand Souls, Common Gems for Common Souls, etc.) a soul gem not being used to its fullest capacity could be considered a waste. Losing a Grand Soul gem because you used the 'petty soul' contained within to recharge a weapon for example. Hopefully the 'soul gem empties when dropped' is not a glitch, but rather a feature intended to aid in avoiding such wastes.

Leave FILLED grand/black soul gems at home. They weigh more, and you won't want to use them out in the field to recharge your enchanted weapons as that'd be overkill. Just go pick them up when needed for casting new enchantments.

Make sure you have a supply of UNFILLED petty/lesser/common/greater soul gems and then go on an occasional soul trapping spree. I have a backup weapon with the soul trap enchantment for this purpose because casting Soul Trap is a nuisance. The fact that you have unfilled supplies of each soul gem type means you don't have to pay attention to what type of soul you're trapping -- it will just automatically go into the smallest gem that can hold it. When you see the message that says you didn't have a gem large enough, that means you've run out of empties: your spree is over, go back to your primary weapon.

Buying unfilled soul gems from a magic vendor is a good way to make them have enough money to buy your jewelry/etc.