What do you do when you have very little action in a large amount of time? (An example would be a long journey). Or vice versa?
First of all; Little action in a lot of time. There are no definite remedies for this, and it doesn't necessarily need a remedy. However, there is a couple things you can do.
One; Look for certain places where you could expand on a subject. You can take a short sentence, like this one;
They lost their way several times, but they managed to travel 20 miles before dusk.
And turn it into something like this;
Earl thought he heard people talking, so he and the rest of the company went to investigate. After attempting to find the source of the voices, the only thing they found was that they were lost. They wandered for about an hour, but with a little help from Gerry, their tracker, they managed to find the road again and continued on their journey.
You can expand that even further, but it is advisable to avoid short diversions from the plot like this, if it doesn't add something needed to the main plot. However, you could write a chapter in which they get lost and find something that will effect the ending, such as a new character, a strange, ancient tablet with undecipherable writing on it, or the remains of a sharp-toothed Kreer.
Another thing one could do is make more obstacles. The obstacle is completely up to you, but it would be good if they followed along these lines;
-The person (or something else) causing the obstacle does not want your character to achieve his goal.
-It should threaten your character's mission
-It should be mostly unexpected (I'll post more on that later)
On a side note; Your character's goal should be plausible. In other words, the goal should be worthwhile enough that the reader wants your character to achieve it.
What about a lot of action in a little amount of time? This usually isn't a problem, but if you have more than one POV (Point of View, where there is a different character narrating), you may have a problem switching around POVs during a hectic scene, which is why that is not advisable for first-time writers to use that, including me. It also may be better to use first person to narrate, which will remove the possiblilty of multiple POVs.
So, a summary of this tip (for those of you who either skip to the bottom or just skim through it), would be; When you have a little action in a lot of time, try expanding on certain subjects, and creating more obstacles to delay the character from his/her goal.