Heya, the most important thing ive found is to make sure you have good paint and brushes, they dont have to be top of the range but your going to struggle heaps if your materials dont do what they are supposed to.

Its important to find a scale that works well for you, i found that if i worked too big it was hard to make stuff look right and if i worked too small i couldnt put in the details i wanted to.

aside from that its just a matter of experimenting and working in thin layers. start off rough and refine with each layer, dont try and make it perfect from the first layer

I start off with the midtones of say the skin, then add the layers of browns/ reds/ blues to make the shadows building them up gradually to the right darkness then i add the highlights. its the highlights that makes the image stand out.

also its really important to have a good reference photo, make sure it has a good range of tones, its hard to paint something if the image is too light or dark.

I hope that helps some!
and cheers for the compliment