Do I make the players go through the journey post-by-post, even through sections I don't have anything planned for?
I don't know how much I like this option, it seems like it would become very grueling for both me and the players to keep up a post per day rule if no one has anything to talk about. I mean, roleplay can come to the rescue here, but how much are the players going to enjoy that after the first few days of it? I know that journeys like this realistically WOULD be boring, and grueling, and repetitive disregarding accidents and things of the like. But that doesn't seem like the right thing to do in the interest of fun.
Do I plan something for every leg of the journey?
Now, typically there are things to do along the way. But a constant stream of events and combat doesn't seem likely unless the players are being actively hunted or are doing something that causes aggression everywhere. Or perhaps the players are doing the hunting, and the prey are actively trying to escape. This is an option with some merit, but only if the circumstances are right.
Do I 'fast travel' the players where they need to go, or give them a portal of some kind?
This is the laziest option. Don't worry about that "journey" crap, we have more important stuff to do. Okay, the portal option is just a terrible thing to do unless that somehow ties into the plot. The fast travel thing I might see working if it was something like this.
"How are you going to travel?
a) Fast and Reckless
b) With mild precaution
c) Slow and very cautious"
A system where the players decide how they're going to travel, and I write back with the consequences of their choice. And even then I don't like it. It doesn't feel right, and it's just not fun. But it ties into our next question:
Do I skip to the interesting bits?
I've seen this way played quite a bit, but I've got a problem with it. By summarizing the journey and jumping right to the meat of it, you've destroyed a lot of opportunity. The biggest problem I have with this is that it makes it impossible to create a suspenseful or mysterious section. The players know that if you skipped to this particular point in time, something important will be happening soon or very soon. You can't hide it. You lose all the wonder of the moment you had been hoping for. The players also lose chances to develop their relationships. Doesn't it seem odd to come out of a several hundred mile long journey with someone and not feel any different about them?
Do I give them interesting travel companions with a subplot, so that the story follows them?
This is another option I like, because it you aren't losing anything with it. Everyone is interested and involved in a story, (Well, at least if I'm doing my job right.) so things don't seem quite as slow, and I don't miss any opportunities for subtlety, AND the travelling gets done. But there isn't always going to be an airship journey with a volatile crew, or a trading caravan going the same way as you. But once again, this is a situational option.
Do I give them a very difficult to maneuver environment with constant challenges?
This would be something like scaling a mountain or traveling through a cave. But not every path is a mountain or cave. Why take the hard road if there is an easier one?
Those are the options I've thought about so far, and short thoughts on each one. Being a good DM probably means that your characters are going to be in a situation that makes things interesting before they have to travel. But I'm newer to the role of Dungeon master, so I'm here to get some feedback/ideas. Feel free to give me tips, or post unconventional solutions of your own. I appreciate any help I can get.