A light touch goes a long way. Use small sweeping strokes to keep the paint from pooling and eventually dripping down the glass. Apply the spray paint in thin layers, leaving each layer to fully dry. If you don't you will get pooling and an uneven application.
We soaked ours in the sink for a day then took the labels off. Make sure to get spraypaint that is ment for glass/multi-purpose. We did 1 very thin layer, let it dry and added 2 or 3 more layers. You want to make sure keep the can about 2 feet from the bottles otherwise the paint drips and looks really bad. Hope that helps!
We did this at our wedding, you want very fine sprays, in multiple layers. Some colors finish a bit nicer than others, just an FYI. Make sure that the bottles are completely clean with no label residue, I removed them using goo gone. Then soaked in hot water and dawn for a few hours. Do not start spraying right onto the bottle, like with any item, start spraying and then sweep over the item in smooth and steady strokes.
We stuck a stick in the ground and turned the wine bottles upside down so we could get everything without having to touch it or rotate it. Multiple thin coats came out way better then trying to soak the whole bottle in one coat. Spray vertically for one coat then horizontally for the next.
Great advice. I would add - don't hold the button down once you paint a stroke. Press, stroke, release, repeat. Wear rubber or latex gloves, protective eye wear and a face mask for protection. Make sure you are doing this in a very well-ventilated area. Outside is best.
BTW, if you are spray painting with metallic paint, you can't seal it with clear sealer spray or brush on paint, as it will dull the metallic sheen.