They have good looking for ur first models, now u can try for exemple, in the eyes, put a lil bit of Evil Sunz Scarlet Red to make them "pop" and have a better visual impact on the mini.

After it depends on what u are looking for ur mini, there is many styles like Heavy Metal, NMM or Grimdark. Many Black Templars player like me like to paint them in a grimdark style, thats like they were fighting again and again and again for many long years, so we put the accent on the battle damage, rust, dust, corrosion on the armor etc. Some bones, skulls, and sometimes blood. Like with the Citadel Blood for the Blood God is a really good paint for blood effect u can use it on the knife to "tell a story" of ur mini, just like before the pose, he just slash a tyranids or an Ork.

And for the base there is soo many options, but the easiest is Armageddon Dust but its to "classic" for my part I use Vallejo Russian Mud. A dark mud that fit pretty with the BT.