>>1148079Prep your model before hand, wash it with soapy water, remove any flash, fix any problems, make sure the model is damn near perfect before you put on any paint or it will be damn near impossible to fix later.
Prime your model.
If you are airbrushing, multiple light coats is always better than one thick one that will obscure the detail. Consider preshading as well.
If you are brush painting, thin your damn paints (almost as thin as full fat milk) and do multiple layers, each with perpendicular brush strokes to the previous layer.
Remember, masking is your friend, but get tape that's meant for models; regular masking tape with wreck shit.
For scale models, you only want to do pin washes (to pick out panels) rather than wash the entire model.
Once done, seal the model in a thin gloss coat (or just to the areas you are going to decal). Once dry you can now apply the decals (a gloss surface prevents rough paint surfaces from trapping air and causing silvering); consider using a decal setting solution. Once done seal the decals again.
Now do any weathering and finally apply a matte top coat.
For more information, check out the gunpla threads in /toy/ and /m/ and the scale modelling general in /toy/.