Best practice is preventive, get your surface sanded to about 400 grit and wash it well to remove dust and grease. Also spray in as low humidity environment as you can get, under 60% at least, as the spray hitting a moist atmosphere can definitely cause that sandy look as the paint clobs up with the moisture it hits midair. Also too hot of an environment can be equally problematic with the paint drying some before it hits the target, though this is less common except for super quick paints like laquers. Also have a little bit of airflow from a fan or something, not so strong it blows your spray off course, but enough to evacuate the overspray cloud away from lingering around and dusting back on the helm. Also also, don't hold the can too far while spraying as it cause also lead to drying too much midair, 6-10 inches is usually good.
To salvage this though, yeah, just wet sand it, will probally need to respray after. Steel wool might work too letting you not need to respray.
