Soo... I recently booted up Morrowind again after a long break after beating the main quest and some Hlaalu and Morag tong quests.
I finished the main quest at around level 11-12 due to having Mehrunes Razor, two levitation items and alot of potion boosts. (And some fiddling around with the difficulty booster at Dagoth Ur)
So.. I arrived at Mournhold and I'm trying to do the first quest, but the freaking goblins keep killing me. I can do alot of damage to them, but they always drop my health down to zero very quickly.
I'm playing a custom stealt class Dunmer. Almost full glass armor and wraithguard and keening equipped. I'm level 14 atm.
Other than levelling, what could i do to improve my character?

Tribunal is meant to be started at level 20-25

Yeah as Pluto said its meant to be for higher level characters. But also, dropping the difficulty to beat bosses isn't quite going to help you in the expansions. You need to put the time in to level your character up.

Adopt disabling techniques. Try using spells or enchanted weapons that Damages their Strength. This way they not only loose combat ability, but if you damage it down enough to zero then they cant run after you! After that you can casually pepper them with darts/arrows, summon minions or just slash em up.

Or failing that try and work on sneaking past (although from memory Goblins are rediculously aware of their surroundings :/ )

Well, since the problem seems to be the goblins doing too much damage for you to keep up with, I would say you have three potential ways to overcome this:

1. Increase your health pool. This one would normally be handled through leveling up and making sure you've maxed out your endurance. There are other ways though, such as making fortify health enchantments or potions. I wouldn't advice on this though unless you intend to abuse alchemy to make a potion that lasts virtually forever. Fortify Health is an infamous effect for killing of unsuspecting beginners who don't realise that the amount of health added by the spell is removed after the effect fades meaning that unless you have more health left than you added then you're doomed.

2. Lower their damage. This can be done either by increasing your armor rating (getting better stuff or training your skill), or by damaging their strength like suggested above.

3. Stay out of their reach. This requires you to have some sort of ranged attack, and to be faster than they are. If you've completed the MQ then you should have Azuras ring with a CE restore fatigue effect. With this you can run away at full speed while still keeping your fatigue maxed out so that you can hit your targets consistently. This requires some manouvering space and preferably some Damage Speed effect to keep things under control but I would say that it is your best bet other than simply leveling up and getting tougher.

All in all I would say that the best thing you can do is follow the standard RPG strategies for not getting eaten alive by the big bad monsters: If something keeps killing you over and over then go do something else. Kill some weaker monsters, do some other quests, gain some levels and some equipment and then try again.