At work last week I was trying to draw a cramped small space with a lot of clutter in it. That's one of those kind of drawing challenges that nobody ever talks about and it can be difficult to know how to dive into something like that when you are first starting out. As usual for me, I drew it and redrew it until I came up with something that worked, and after I was done I could articulate how I ended up making it work, but unfortunately I couldn't have told you how to do it before I started. Anyway, hopefully if I write it down I will remember how to approach it next time and maybe I will save you the hassle of blundering through it yourself.
Of course, there's no great secret here, just use the same design principles you should use when doing any kind of drawing. Firstly, use a good variety of small, medium and large shapes. If the clutter is all small shapes it will look too busy and fussy and be hard on the eyes. All large shapes and it starts to lose the feeling of clutter, and it might start to look like the camera is zoomed in real close or that the space around it is real small, like we're looking at a collection of stuff in a shoebox or something. Also, variety and contrast makes any drawing more interesting, so that's the best reason to use a mix of differently sized shapes.
Although we're trying to draw clutter, you don't want to cover every inch with detail. It's important to remember to leave some blank areas for the eye to rest (these could be the large objects of clutter we talked about above). If every last piece if the drawing is covered with shapes and lines the eye will get tired very quickly. Remember that lots of pencil mileage is not the best way to convey a cluttered space. Also, the blank areas will provide contrast to the really cluttered areas and, ironically, make the space feel more cluttered by comparison.
Also be sure to use a variety of types of shapes - round, square, and everything in between for nice visual variety. And here's the key - and the hard part - plan out your drawing carefully so that no round shapes are next to (or overlap) other round shapes, no square shapes are next to (or overlap) other square shapes, etc. I think that this is the most important part: spacing out your shapes so that you have enough variety in shapes and also so that no similar shapes touch or are near each other. This is the biggest factor in keeping the drawing from looking like a confusing mess of lines that don't add up to anything.
Surely there are better examples of clutter drawings but this is what I had handy. Ken Anderson drew great clutter. It's worth pointing out that usually when you are drawing a cluttered environment, it's in service of describing the character and personality that inhabits the space. Notice how all of the items scattered around Roger's house describe the fact that he's a musician and also hints that he's a bachelor - there's no feminine stuff at all. speaking of which, he drew the Dalmatian (below) anatomically correct for some reason(click to see these all bigger).
Also, don't draw any lines that are parallel to each other, or to the edges of the picture frame (in other words, straight up and down). Parallel lines denote order and if you want to indicate a confusion or a mess, make sure that all the lines point indifferent directions.
From the Famous Artist Course - Robert Fawcett takes about creating confusion in a drawing by making sure all the lines point different ways. Click to see bigger and read the caption at the bottom.
A great sample of clutter by in a Bill Peet storyboard from "Sword in the Stone". Here he did all the above and also relied on tones to help separate the forms from each other and also to eliminate having to draw detail on the forms that would have been distracting. This panel is a closeup of Merlin's workbench with a bunch of models, and notice his use of everyday objects in the frame to give it a sense of scale so the viewer won't think that they're looking at a collection of real full-size trains, boats and airplanes.