Then my best piece of advice to you is to go play games. Seriously, go check out the list of games on MMORPG and play games with high ratings, low ratings, no ratings at all. Don't read up on the game besides what you can learn from it on the mmorpg website, just jump straight in and play. I would suggest you sink anywhere from 5-10hrs in a game, plus time for each feature they have that is unique for the genre(housing, marriage, breeding, etc)
But along the way.... keep your eye on how you feel during the sign-up procces, character creation, the first few minutes of the game, after you leave the starting level. Anything you're really enjoying, anything really really starting to annoy you? Write it down.
And after you've played through a dozen games, any features that make you go, "Ugggh, whyy?" each time you see it?(for me it's usually the tutorial). Any times you find yourself going, "oh my god this is awwwwwesome!"(mother fucking hoverboards in Wildstar). Anything you kinda like is there but just wish had a bit more to it? Write it down.
Most MMO designers I see have played one or two, or maybe even a dozen mmo's in their life-time before they get to work. Which is not a bad thing, but I think it is really, really important to get a nice view of what is possible. Sure you've got a few great ideas that are all your own(don't tell anyone, it might get stolen!), but what about other parts of the game that you have no real ideas for... just yet? If you plan to use a system similar to another game(which is totally fine), make sure you understand that system and the ways it can be implemented to be sure it is a right fit for your game.
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Say you want to have housing, it doesn't seem like it will be a big part of the game to you, so you don't spend much time on it. But lets look at it anyways. There are many, many types of ways you can have it. Lets take Runescape and Toontown as two examples.
Runescape's housing is very customizable, and can offer a player a lot of convience for skills as well as a fun place to hang out with unique ways to build those skills. You start out with a room or two, and can build items inside the house, or build new rooms/areas. Building takes resources found elsewhere to do, and is it skill in itself that limits what you can build at the start.
Toontown's housing is semi-customizable. You get a plot of land for you and your characters(max of 6). There are already 6 houses built. Each house can have a garden which can grow the consumable attacks for the game. Inside the house you can place furniture where ever you like. On property you can have a pet that can be trained to heal you in battle, There is also a fishing hole with fish unique to housing areas, and special health bonuses to heal.
Runescape's housing requires a lot more thought and effort on the behalf of the player, but also provides many bonuses causing a supply demand system with fewer players having what many want. This opens the gate for people spending time at other's housing(maybe being charged for it), but those people not nessisarily being friends, there only to skill-up.
However Toontown's focus is more on housing being a quick place to heal-up and rest from battle, but also becomes a place where people tend to hang out together even though there is very little anyone can do to advance the character there.
That is because Toontown seems to get players to focus on friendship, though you never feel forced to do it(people working together to kill a mob does not dimish XP earned, it simply speeds up the process). Where as Runscape is heavy on all it's many skills that need leveling up, and since housing is a good place to do that, it causes a setting where people are not leveling together, but seperately near each other where companionship may happen, but only on the deliberate effort of the players. However, housing is a great place for player formed guilds to start. Players working together to raise supplies to build a large house they can all share and use. Is one better or worse? Not really. It depends on your game's focus. But you wont know about either of these systems well just reading about it, you've got to get out and play it and see how it feels for the player.
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My next big piece of advice to you is do not let yourself stay designing in one spot for long. Spend some time hashing out that super cool cooking system, or the political system. Spend some time sketching out game screens. Look around the google images search to find the art style that fits. Get a level editor and make small versions of towns or starting areas to make sure your scale is correct, that the area doesn't feel too empty or full. Think up some lore for the game, why is the world the way it is? Create small flash games to test out different systems that you have in place(say political, or crafting) and have people test them to see if it's fun.
Basically, don't let yourself get bored. Designing an MMO is a lot of work, especially before you are in the phase of "lets build this baby!" You don't want to get burned out before you've even begun. Not only that, but you don't want to create this amazing cooking system that simply does not fit into your game anymore.
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My third and final piece of advice to you is, don't let other people get you down. Understand that everyone wants to make the next big MMORPGFPSTDSRTS(you get the idea). Now that's not a bad thing, but too many of those people come to sites like this asking for advice on their game, afraid to reveal too much for fear an idea might get stolen. Then get upset when they are told how impossible it is for them to create an mmo. Is it impossible? Nearly, but with effort you and a small team might do it. But if you've just begun hashing out your big ideas in the past month, it's not time to build that team yet.
And please, please share your ideas. No one is going to steal them. Lets say you had a cool crafting system. For someone to have to steal your idea in a way that would hurt your game, they would have to not just take the base idea, but plan out all the types of ingredients, assign them numbers, balance said numbers, figure out how it works in the rest of the game, program it, create art resources, etc, etc,etc. That takes time and effort, and I can assure you by the time they are to the end of that process, their finished product will look nothing like yours and play differently as well. Not only that, but the risk of the above happening is so low, and would do so little damage to you game. Whereas sharing your ideas can have them grow to levels you didn't think of, or can help you realize that maybe the idea doesn't work well in your game after all.
However If you are going to share ideas, be prepared for them to get shot to pieces. However, be aware that this is a very good thing. Hopefully you get into the habit of destroying your ideas yourself, The thing is, when it comes to gamers, they are very picky and very harsh about it. You want a system that encourages interaction, but you don't want a system that will allow players to grief each other. You also want a system that is a lot of fun, but not too complicated. Getting fresh eyes on your ideas can really help you see things at an angle you never thought of, and better it's seen now, then when it's been put into the final game and you realize a major flaw way too late to remove or change it much without redesigning much of the game.
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That's really all I can tell you right now, as a person who's been working on designing an mmo for maybe eight years now with not much to show for it beyond gigs of mini-prototypes, yards and yards of word documents, and tons of pictures, these are the things that have helped me. Game Design is my favorite hobby, I can't play a game without seeing all the little ways it's been put together and how it effects the players of different levels and play styles. At the begining I wanted to make a game right now, everyone help me. Now? I don't particularly care if the game gets made, the fun is in the design for me. Plotting out my version of the perfect mmo with little regard to scale and how much it would realisticly cost me to create. However if I ever do win the lottery, you can expect my game to be the next WoW Killer ;)
