I looked on YouTube for 'painting miniature figures' and got a pile of hits. About half are 32mm gaming figures but the same techniques should work on 52mm military stuff. Bigger stuff like 90mm might take some adjustment. 

Frankly you're lucky. When I first started out I was trying to go by photos in books and magazines- watching someone do it on YouTube is much, much, easier. 

I like the technique Verlinden developed.  Good reference here.  https://www.abebooks.com/first-edition/SYSTEM-Volume-Figure-Painting-Verlinden-Lette/30331203176/bd

I got a set of facepaints by scale75 and found its guide to be pretty useful. I followed it at first but then ajusteded it to suit what i wanted. mainly its just a case of getting the base colour right and then going from there, building it up.

The one thing i found that helped most was painting some larger scale (1/9th) busts. I can try out thing on the larger scale and then use that on 35th figures.