Make it bigger. When you're designing clothes in cloth, you need to think of each panel as a piece of cloth, that are stitched/sown together. The area between the stitches becomes zero (or at least close to that) when you start simulating. So if you have a pants leg whose panels are only a little wider than the leg, may look more than wide enough before simulation. But as soon as you begin simulation, the stitches will shrink and the pants leg will become tight (and uncomfortable too for the poor cg character).
Another thing you might note is that for the clothes to hang correctly on the character, they need to be sort of correctly designed. You almost need to be a tailor to get this right, but a little (i mean a lot) of tweaking will get you there in the end. Some sewing magazines and books might be a good reference for this.
And on a final note. Getting cloth in Maya (or most other cloth simulators I've seen) to work perfectly is very hard. Parts of the cloth will jiggle about if the character stops moving for a while, it won't look like the right type of clothes etc. etc. I even had a bug once with Maya where Maya ignored the properies I'd set for a garment once I reloaded the scene. And it's dead annoying seeing those cloth demos of women dancing around in flowing dresses, there is too much movement to see if any part of the cloth is behaving weirdly, and flowing dresses are much easier to do than say on ordinary shirt. An old guy playing chess wearing cloth clothes will give you a much better picture of if the cloth is working or not. 
Ragnar
