I've never really played UO before, is there anything a first timer should know?
...there are so many things it's not even funny. First thig is going to be learning the game interface, which if you've played any game made in the past 15 years will be totally unintuitive. The game world and inventory and things are analog. No "inventory slots" and things can be dragged to/from the ground to your bag. Double click on tools to use them and click on targets. For example, you can cut up clothing by using scissors on them to make bandages. You can use a dagger on deer corpses to skin them to make armor. Skills and attributes increase from use.
Some default useful commands:
alt-p paperdoll
alt-r radar map
alt-b spellbook
alt-i inventory
alt-k skills
Right click on windows to close them. Click and drag on people, npcs and monsters to bring up health meters. Strength = hp, dexterity = melee attack speed and stamina, intelligence = spellpoints. There are a fantastic number of things you're just expected to know. Some of the game interface is used via chat. For example, if you walk to a bank and say "bank" it will open the bank box. If you stand on a teleport and say "rec su" or "rec du" it will teleport you up or down. You can name your pet Bob and say via the chat interface "Bob guard me" and Bob will guard you.
Early game survival advice:
Tame some pets. It will only take a few minutes to train animal taming enough to be able to tame a cat or dog, which can improve your otherwise early game absolutely helplessness. Macro your hiding skill (alt-p,. options, lower left button, add) and train it a lot. Hiding makes you invisble, sort of. Mostly. Very helpful, but (at least in this version I think) you can't hide after you've been targetted. Still useful. Train hiding.
Individual skills start with a cap of 100 and "total skill points" are capped at (1000 I think) and you can freely train any skills up until your total is that level, at which point to train anythign higher you have to set something to go lower when something goes higher, so your total never exceeds cap. Skills become more difficult to train at higher skill levels, and anything can be trined for gold up to 33 (I think), so if you want to minmax, choose two starting skills at 50 and one at 0. Take magery, no matter what else you do, you will want it at least to a certain level so you can recall. Recall allows instant teleportation to ANYWHERE in the world, via the mark spell. This is awesome. Boats and houses exist, but are expensive. The game will try to kill you.
Very hard.
Players will kill you. MOnsters will kill you. Invisible things will one shot you. The game is not gentle, and you DO NOT keep your stuff when you die. On death, you corpse creates a container with all your stuff (possible expceptions, version dependant not sure yet here) so that any player who kills you can take it. If they don't, you can run back to yoru corpse and recover dropped items.
If people are really mean they can cut up your leather and cloth armor and leave the shreds to mock you. This game is merciless.
Lots of things a new player needs to know. This is not a complete list. Spells require reagents. You can't cast spells with weapons equipped. Macros are your friend. Moongates. LEARN the moongates. Players can steal from each other. If there's anythign in your inventory you absolutely dont' want stolen, put in a bag (bags can nest) with something heavy like deer hides on it. Oh, deer are called hinds. Stamina is used up when you walk through things. If you have stamina, you can't push through things. This means you can get trapped, even by your own pets or other players, even invisible players...and die because you can't move.
...so much...
But it's a neat game.