A texture is very important for a 3d asset if you want to add further details. You can choose between photorealistic textures and handpainted textures. If you wanna create a handpainted texture you need to find an artstyle and some guidlines. I will show you in this tutorial how I am doing my textures for lowpoly props.
I made this with Blender 2.79, Photoshop CC and Unity 3d.
This post includes all parts of the video tutorial series: