Keep the weather in mind. If it is cold, you will need pants that are thick and can keep you warm. This will be crucial that you wear proper pants for the conditions. If the weather is warm or hot, it is best that you wear cotton pants that can keep your legs cool. Keep the conditions in mind when buying pants.
Keep the terrain in mind. If the terrain is normal, you can wear anything that keeps you comfortable. On the other hand, if the terrain is rough such as rocky or the ground on which you move is thorny, it is best that you get pants made of a thicker fabric. These may be a touch uncomfortable but they will protect you against scratches and cuts as well.
Beware of these little critters as well. They can cause a fair amount of trouble and you do not want to get bitten by them. Most of them will only cause a bit of discomfort while there are some that can cause illnesses as well. Wearing thicker pants will help you in avoiding this bites and do keep this in mind if you are purchasing a pair.
The time to spend on the trip
The pants that you will buy will also depend on the time that you will be spending in the outdoors. If the trip is a short one, you can probably use something from the last trip. However, if you are undertaking a trip that is in a different terrain and will take a longer amount of time, be sure to grab a new pair of pants and get one according to the specific requirements of that area.