[Mr. Business]

You could try my (not) patented technique that I used to create a few Zombie City Tactics maps. While ZCT ain't a platformer, it works similarly enough that this technique could be used to create a few interesting jumping puzzles or tightly-packed hallways:

First, choose a short phrase like "fuck you" or "waffle taste." Now, using your map editor (assuming that you have a GUI map editor. If you don't, then this method might be overly time consuming), spell that phrase out in one basic block type on the screen.

Now that you have your words all blocked out, begin arbitrarily removing blocks until the phrase is no longer recognizable as such. What you should be left with is a rather random and usually fairly diverse arrangement of blocks.

Once you have the blocks arranged to your liking in a relatively random pattern, go back through and add details, change which blocks are used where, and generally spiff things up. I can't really help you here, but my best advice is don't overdo it on the variety of blocks. The block arrangement shouldn't look like an exquisite-corpse drawing.

Also, as a general rule of thumb, I notice that a lot of platforming games force the players into cramped, close combat situations. Hallways that are narrow, vertically or horizontally, are pretty great for building tension in the player.
_________________
Taking a break.

[Mr. Business]