I recently joined a group of Japanese plastic model fans who meet about once a month in Ogikubo (荻窪) near a famous plastic model shop called Kiyahobby (喜屋ホビー).
On my first day, I was lucky enough to meet and talk with one of the most famous plastic modelers in the world, Mig Jimenez, who was visiting Japan from Spain. I learned a lot from him in just a few hours. I also learned a lot from my new Sensei, Masahiro Doi, who guided me during the application of a surface primer (Tamiya TS-4 German gray lacquer air spray) on my plastic model: an Sd.Kfz.232 German 8-wheeled heavy armored car (Tamiya, scale 1/48). The trick to obtain an homogeneous surface was to apply the air spray with quick strokes. After applying the German gray primer and letting it dry for about 30 minutes, I started painting the shovels, the wheels and the turret. For that I used Vallejo acrylics.
On my second time, Doi-sensei guided me through the process of weathering my model. I started by applying a wash of Tamiya XF-64 Red Brown enamel paint (diluted with about 2 times of Tamiya X-20 enamel thinner) using Tamiya modeling brush HF No.0. The goal here is to give some depth to the model by darkening corners and making the surface more realistic. Then, I removed the excess of enamel paint with a Tamiya craft cotton swab using up-to-down strokes for expressing the aging caused by rain. Once the enamel paint was dry, I applied Mr. Weathering Color Sundy Wash (diluted with Mr weathering color Solvent 110) on the wheels and lower parts of the car to emulate dirty and dust. I used a slightly bigger Tamiya HF modeling brush (no. 2) for that. The result is what you see above!!
Conclusions: I think there are many ways to improve the result, but it's probably good enough for the first time. In the process I learned many things such as the difference between lacquer, acrylics, and enamel paint; or the typical steps in the painting sequence. I also learned that there are many magazines and blogs explaining numerous tricks to make your models even more realistic.