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When preparing for trip to the mountains, keep in mind the temperature, altitude, season and schedule.  Depending on which mountain region you're ascending to, some clothes may be more appropriate than others.  Here's some quick questions to ask yourself when packing for your next mountain excursion:

1. What season is it?  If it's winter, it will be more appropriate to pack warm, waterproof, winter clothes.  If it's a shoulder season (fall, spring) you can plan on the temperatures being a little cooler than lower-altitude areas.  But, if it's summer, then you may want to pack light clothes with a lot of sunscreen; the higher you are, the closer you are to the sun and its harmful rays.
2. What activities will I be doing?  If you're just going to the mountains to get a little R&R then I suggest packing sweats, comfy jeans, sweatshirts and cozy shoes.  But, if you find yourself rock climbing, snowboarding, snowshoeing, hiking or mountaineering, you'll need to pack appropriately. 
3. Dinner plans?  In higher altitudes the temperature is capricious, changing at a moment's notice.  So, if you plan on going to dinner on most nights, make sure to pack some warm, appropriate clothes.  I suggest nice, comfortable jeans or slacks with a nice long sleeve, collared shirt and a good looking windproof jacket to keep you warm on the walk from the car to the restaurant.