Cooking time: Use the original cooking time as a reference point for how long you should cook the altered recipe, monitoring closely for the results you are looking for. If you are baking half a recipe of cake, bread or pie, then the cooking time will be more than half-about two-thirds to three-quarters.
Pan size: Your best choice is the pan that comes closest to keeping the ingredients to the same depth as the pan originally called for. If you are halving or doubling a recipe, use a pan that has half or double the volume of the one called for in the original recipe.
If you cannot keep the pan contents to the original depth, then adjust the time, temperature and amount of liquid accordingly. When the contents are deeper for dishes that have a lot of liquid, increase the time and use a little less liquid. When they are deeper for baked goods, increase the time and lower the temperature slightly. When the contents are shallower for dishes that have a lot of liquid, shorten the cooking time and add a little more liquid. When they are shallower for baked goods, shorten the time and raise the temperature a bit.