Sure thing- here ya go:The first thing is to get a feel for a good story. The best way to do this is by reading books, and following the plotlines carefully. You want something exciting, something which will keep a reader's/ player's interest and which, for minecraft, offers some challenge, both in terms of puzzles and frantic action. You will want an environment which hooks the player into the map (a dangerous spawn location etc). If you need an example for a good storyline for a map, then you should take some time to play a couple of the more well-known maps which are known to be great. I haven't played any adventure maps myself: I have learned about storylines by reading books since I was tiny :P
Regarding buildings- this is where I usually spend the most time. I would recommend going with simple buildings, an rich environments. If you take a look at NPC villages, you will see the simplest form of buildings. They are too basic in my opinion, so perhaps start with those buildings and edit them a little. In the well known maps by Vechs, his buildings are remarkably simple, although you should try for something a bit better: his style is CTM and not adventure map. It's always worth searching through screenshots for maps posted on a site such as this one for inspiration.
When I make a map, I get the rough storyline set out, missing the details. I then start to build the beginning of the map, and I get a sense of what is needed, what is missing. I then add whatever I think is required, and move on to the next area.
I use a few mods and programs external to minecraft when making maps. The most useful is mcedit, then singleplayercommands, then toomanyitems. I occasionally hop onto a privately hosted bukkit server and load up the map and use the voxelsniper plugin to create awesome environments easily.
The best tip is this: Make up your own mind on what is important in a map. Do not take anyone's opinion for your own. Read around, read helpful passages like this one, take a peek at buildings made by others, in minecraft and in the real world. Once you have an idea of what makes a good adventure map, then go for it! And have fun- that's the most important thing of all.
-KROSE

Sure man :) The final version will be out out about mid-Summer. I'm doing an entire map re-make with epic surroundings: not just a plain boring vanilla world. I'll make sure I provide both links when it's out :)

I'm just about to update this post with my latest demo of the map (number 3). A whole new area has been added, the landscape improved, and a few secrets added too. I've added in an iron golem in a secret portion of the map. Also added a railway station which unlocks once you progress through the map. I'd love some feedback for it!