First painted mini. Asking for feedback and tips for the next!

Hi! I've always wanted to paint a Warhammer 40K miniature. This year, I finally decided to go for it and subscribed to the Combat Patrol collection! After watching dozens of tutorials and reading advice from people on Reddit, this is my first painted mini!

I know there's plenty of room for improvement, so before I start working on my next Infernus Marine, I'd love to get some advice on which areas I could improve.

I used Vallejo Xpress and Vallejo Game Color paints over a white primer. The shoulder pads were a nightmare because the yellow Xpress paint pooled around the edges, and I had to apply multiple layers, making the paint too thick.