I've never really played a stealth character before; wouldnt there be some cases where stealth is impossible? Like for example you enter this room full of light with a boss in it. How would stealth come in handy then? Or would the stealth character need to go for head-on fighting?

For some reason in dungeons, even in a room full of light, you stealth better than outdoors at night.

The only situation where I cannot stealth is a dragon fight. Because in order to get them to come down, they have to see you. If you remain stealthed, they'll never land.

Most times you do some research first and look for several shadowy spots around the place and paths between them that go around corners hopefully. Then you aim a sneak shot at the guy, and run quickly while sneaking to a new place, and wait for the guy to search thoroughly the area you just were, and when your sneak eye says "Hidden", aim another sneak shot at him and run to a new place. Repeat till dead. Also if the guy can regenerate health or can heal himself, a damage health over a period of time poison or a damage magicka over time poison are useful additives to your first sneak shot. Also you will want to get an invisibility spell in case the path to your new shadowy spot is out in the open, or you are unsuccessful in any way.

you put on the heaviest armor you can find, take a companion with you, a big fancy flaming loud spell in your hands or a gigantic battle axe and then you run loud screaming through the dungeons - this way NO ONE will recognise you - guaranteed

Try stealthing a charging Steam Centurion...

This explains so much. I was wondering why I couldn't get them down sometimes. I frequently out of habit sneak when enemies are nearby.

i have killed a dragon all stealth (and bow). its just bad if there are enemies anywhere close, hell fly there if the doesnt see you.

Ask http://www.uesp.net/wiki/Oblivion:Gogron_gro-Bolmog, I seek his advice first and foremost on matters of discretion.

If you have Sneak at high enough level, you could just take out all the falmers in the dwemer ruins with sneak attacks. Even the Centurion couldn't do a single hit on you, by swapping place to hide and keep doing the sneak attack (by bow in this case). But stealth character losses its effectiveness when it is in an open fight where you have no place to sneak or hide.

When in doubt, use invisibility potions.