Creating textures

I can handle Blender pretty well and get my models into the sim OK. The only thing Im not very pleased about is the quality of the textures I use.
I look at the commercial scenery and am amazed at how realistic the textures look.
What’s the secret??
I don’t expect a full-blown explanation, but perhaps a link or two as to a YouTube video or a web site that might explain it.
Thanks in advance for any response.

John in Indiana

Texture resolution? Its a bit like Minecraft and Sphax texture packs. Default Minecraft is 16bit? Sphax Texture packs can go all the way up to 512bit. Trouble is the more you turn it up the more the hardware struggles.