First, a list of the medals that can be awarded are
here (click me). Feel free to post to the Idea Box forum with your ideas for a new award or medal!

The beginning of award nominations will be announced here (and possibly on the game via the MOTD) so they can be decided. After a set period of time, the nominations will end and the voting will begin. After the votes have been counted, the award will be given.
There are a couple medals that can only be awarded under special circumstances (the Adventurer's Guild and Idea ones for example), so nobody can be nominated for them. However, the rest are pretty much up for nomination under the following criteria. Please note that you
cannot nominate yourself.
Builder of the MonthThis award can be given to the builder of any zone
currently linked in the live Distant Lands game. This does not apply to zones that are not linked and currently reside on the live game or build servers. This can be either a new zone that was just put in or a past one that you just think is the coolest thing ever. Maybe the zone has some wicked descriptions you like, or some items you think are slick, or maybe it's chock full of RP potential you think should be unleashed. Whatever your reasons, you can nominate that builder for this award. You don't even have to know the name of the builder, just the zone. If you know who built it, then that's awesome. If not, then we can certainly find it out for you. Do note that even if a builder is no longer on DL, or doesn't have an account on the forums, the award cannot be given at this time (I am working on a way to award a builder that, for the lack of a better term, doesn't exist.) This medal can be awarded to a player 12 times.
GM of the MonthThis award can be given to any game master, quest master or generally any staff member who you think does an awesome job with roleplaying. Whether they're currently running an RP or you loved one they ran 5 years ago, you can nominate them. The only catch to this one is that the person you nominate MUST have participated in the RP scenario
AS STAFF. Many of the staff members also have player characters that they also RP with, and for that you can nominate them as RPer of the Month as such. This medal can be awarded to a player 12 times.
Player of the MonthThere's really nothing that distinguishes what can and can't be used when nominating someone for player of the month. Maybe they help you load items all the time. Maybe they're a beast of a tank. Maybe they just sit at the fountain and make you laugh. Whatever your reasons may be, if you think a player is deserving of such an award, you can nominate them. This award can be given out to a player 12 times.
RPer of the MonthThis is the same as GM of the month, except on the player side. The person you nominate HAS to have participated in the RP scenario AS A PLAYER. Read the above guidelines for "GM of the Month" for details.
Helper of the MonthThis one I really like. If you think someone just goes above and beyond to help out our new players, then this award is for them. Whether it's past or present, you can nominate someone who think does an exceptional job at helping new players learn the ropes and get acquainted with DL. Maybe they just give gear to new players to start them off. Maybe they take them to different areas and show them what to kill there. Maybe they guide them through learning their first MUD. Whatever the case may be, if they've helped out new players in some way, they can be nominated for this medal. This can be given to a player up to 12 times.
Like the "of the month" medals, the "of the year" ones are the same, but done on an annual basis.