The next piece of advice is post a decent shot of your next model, and somebody will be able to tell you what technique you need to perfect! Weathering, highlighting and shading make all the difference, but without an airbrush, they are not really possible. One trick you can use before getting that airbrush - go on, don't hesitate! - is dry brushing. You may already be familiar, but just in case:
Use a No. 1 or 2 paintbrush for small detail, getting bigger for surfaces, and mix a bit of your base colour with whichever colour you feel will lighten it credibly. This is not always/often white - play about until you get the habit. BTW, never use the paint direct from the pot - transfer a small amount using the pointed handle of your brush, onto a non-absorbent palette, and work with that - easier to dilute, mix, etc.)
Then take a very small amount of paint on the brush, and wipe it off onto a rag, kleenex, etc, until it will not deposit on anything other than raised detail. Run the brush gently over the area you want to highligh, and you'll see corners, edges, etc, come to life. Especially useful for AFVs, but also for aircraft control surfaces, fabric-covered fuselages, etc.
Sorry if it sounds as though I think you know nothing, but I don't know what you do know! Someone might find that useful, anyway!
Also, buying a good modelling magazine is a major help, because you can learn from what you see other people doing.
and Adler is right - the more you do - take the time, though - the better they get. My only virtue is that I've been doing them off and on for thirty-five-plus years!