It might just be my OCD but I remove all parts from sprues, glue everything together that's going to be painted the same color and sand down every seam on every part and then I put them on scrap sheets of cardboard with tape and paint them let it dry flip them over paint the other side except for car bodies where I put them on a paint stand. Those I'm getting older I'm getting a little less concerned about all the same marks on parts that are not going to be visible unless you pick up the model and examine it which almost never ever do once it's complete.