As mentioned here http://www.gamesas.com/topic/1486563-will-the-elder-scrolls-online-be-your-first-mmo/ it may be a good idea try one or two other MMOs before playing ESO. But if you would rather not do this, here are a few tips about things to expect and look out for that are pretty standard in the MMO genre.
1. You will see lots of other people. Everywhere. Especially in the starting zones right after launch. This may be a distraction until you get used to it.
2. Certain quest objectives will be crowded. Sometimes many other people will be working on the same quest as you are. (more of an issue at launch) So it can sometimes be discouraging when you are trying to kill that 9th out of 10 bat and someone else beats you to it. Some games use "tagging" which makes this easier. Tagging means that as long as you do damage to the mob, you will still get credit for the kill even if someone else actually lands the killing blow. If crowded quest objectives are annoying, just be patient. Things will thin out as you progress in level.
3. The ignore/block option is your friend. You will come across people in your travels that annoy or offend you. Any MMO worth it's salt will have an ignore/block feature. This prevents you from being able to hear "read" anything this person says, and often times will also block this person from spamming you with group or guild invites.
4. Be prepared to see names that irritate you. Even if you aren't heavy into RP (role playing) you will often see names that you think are silly or ridiculous. Many MMOs have an option in the settings that allows you to hide name plates.
5. Learn to browse the UI (user interface) and hotkey settings. Most good MMOs have a very robust UI/hotkey menu that allows you to activate/change/turn off options in order to more customize the game to your playstyle.
6. Know your "role". If you intend to play in a group for dungeon content etc, you will be expected to fill a certain role. In a game with the "holy trinity", this role will either be Tank, Heals, or Damage/DPS. There may be flexibility here, depending on the game, but those are the three roles you will most often see. "Support" is another role that would be a combination of heals, damage, and buffs.
7. Let the tank pull. (if there is holy trinity) A great way to annoy people and make enemies in a group setting is to pull epic mobs as DPS or Heals. The tank is designed to hold agro and take massive amounts of damage. So pulling the mob as DPS usually means that the healer will have to work much harder to keep you alive, and the tank will have to work much harder to "peel" agro from you.
8. What goes around comes around. If you are friendly and helpful to other players, you will find that you will make friends very quickly. The same applies to being rude. If you are rude or mean to other players, you will find that you will be ignored/blocked very quickly.
9.You will often make more money selling items to other players than vendors. In ESO, that means using the Guild Store. Crafting materials and high quality items are usually in high demand by players that will pay well for such items. You can find more info on Guild Stores by doing a forum search here.
10. Don't be afraid to ask for help/advice. You will find that most players will be more than willing to help you. if it is your first time in a dungeon for example, it can be very helpful to yourself and your group to mention that you don't know the boss fight mechanics. More often than not, a group member will be happy to explain it. This also applies if you have learned the content and a group member asks for advice or instructions. Taking a few seconds to explain things will often help the group be successful.
11. Do not ask strangers for coin. Asking for help or advice is one thing, but asking strangers to give you money will get you a bad reputation very quickly and will make it difficult to get any kind of assistance in the future.
12. Have fun. Remember that the main objective is to be having fun. The overwhelming majority of the people you come across are also just looking to have fun People are people and there will always be a few bad apples. Don't let them discourage you, because they are the minority.
That is just a basic list of things to expect. Hopefully other members of this community with MMO experience can add more applicable tips to the list.
This might help as well:
PvP - Player vs Player
PvE - Player vs Environment
RP - Role Playing
LFG - Looking for Group
LFM - Looking for More
WTB - Want to Buy
WTS - Want to Sell
WTT - Want to Trade
OP - Overpowered
FTW- For the Win
Agro - Threat. The mob is focused on you
DPS - Damage Per Second
AOE - Area of Effect - Spells that damage all or more than one mob in a 360 degree or cone area. This can also apply to heals or buffs.
DOT - Damage Over Time - Spells that damage a mob over time, generally on a server "tic". This can also apply to "bleed" effects.
HOT - Heal over Time - Spells or abilities that heal you or an ally in "tics".
CC - Crowd Control - Mez/Sleep/Root - all forms of crowd control.
And a few that are generally used as insults. I advise not using these terms, as they tend to get you ignored/blocked. But just so you know what they mean.
Newb - New player
Nub - Same thing, but meant to be more harsh
Scrub - Bad player
Leeroy - An old WoW name that has become legendary and is used in every MMO now. It refers to a player named Leeroy Jinkins that wiped his party by yelling 'Leeeeeroy! and charing in to a boss fight before the group was ready.
Troll - Someone who intentionally incites an argument. Saying things in chat just to get a rise out of someone. It is a fishing metaphor - Toss the bait out and troll until you get a bite. Most everyone still envisions a troll under the bridge though