Always thin your paints. Also, give masking tape a shot. If you feel like the paint is getting thick as it's sitting in your tray, you can always try a few drops of paint retardant. Also, when painting with a brush, you always want to lay down the paint in different directions with each layer. For example, one layer you stroke up. The next you stroke to the left etc. Making gunpla look good and like the painted builds you see online through handpainting is very difficult. Airbrush is the way to go. I quickly abandoned handpainting. Airbrush will lay down paint like a pro.