Looks like a nice build!
The basics are a great place to start when looking to improve - sanding mold lines (and making sure to smooth out any sanding marks), filling ejector pin marks and sink marks, test fitting parts, cutting parts from the sprue trees and removing the tag, etc.
Do you use spray cans or do you have an airbrush? Each requires some preparation depending on the type of paints used. Getting the plastic on the body smooth, then priming and painting take some experience and experimentation. There are lots of reference materials available online when it comes to paint and building. Don't hesitate to ask questions here, too.
Don't forget your health and safety. Most importantly. Sanding creates dust, paint and glue can be toxic. Use eye protection, dust masks and make sure you spray paint outside or use a proper spray booth so the fumes don't affect others in the house. A dedicated workspace is helpful, but I've had times where I uses a TV tray while I worked on a model and had to put it all away when I was done until the next time. I'm fortunate to have a workspace in the basement now. Take your time and build with safety in mind. Just as important as health...have fun!!