I went outside and clipped a few branches of to use as the wooden part for some trees. Here comes the question....Do I need to do anything to the branches to prevent them from dying out, becoming weak, our changing colour in the future, etc etc ?

Thanks
Leader

One method that I know of it to place the fresh cut branches, with the leaves still on, into a glass of 2-to-1 water/glycerine mix. When leaf edges darken, remove and hang limbs upside-down in a warm, dark area. Than you can cut off the leaves if you want.