Dry brushing shouldn't be too difficult, but if you're running into issues make sure you've got the bases covered:
Use a thick, flat brush. Honestly, a paint chip brush from a hardware store should be fine. You don't want to be using something round and smooth like a water color brush.
Do not wet the brush! Do not use any water at all! To make sure it's "dry" enough, pat the brush off on a paper towel after dipping the brush in the paint. Keep brushing the paint on the paper towel until your brush strokes are clearly dry and not giving full, smooth strokes. Then you're good to go.
Silver paint can be very, very thin. Depends on the brand of paint you're using. It doesn't show up very well unless it's reflected in the light and then it looks very bright. Keep that in mind, and you may want to add some white or black paint if you believe it is too thin.
Post some photos of your attempts! Even if they're "johnny age 3", dry brushing isn't pretty and shouldn't look like a masterpiece. Weathering is messy!
