Try not to handle the glass too much or the foil. When you foil, always wrap the whole thing. Then put extra pressure on the edge first, then pinch and rub. Trying to cut the foil to make a butt joint, always leaves either a weak spot or a non-foiled spot. Try to start the foil on the inside edge of the piece, so there's no chance of the foil lifting from that.
Warm glass is always easier to foil than cold.
A heating tray works well for a bunch of small pieces. Use hot water when cleaning them, it helps break down the dirt, warms up the glass, and helps make it dry faster. An incandescent bulb also works well. Or a space heater. When foiling blobs, lightly grind the blob.