Give the object you painted, to dry completely. Do not try to gloss over the half-dried drips of paint. This can quickly cause the entire painting will have to start over. Be patient and do not rush things.
Place the object so that you can easily reach all areas. For example, if it is a door, remove it and place on a prepared surface. Zone "Stripping" the old paint is better to do more, as it still may smudge and chance anything to smear is still quite large.
Run a sweep of the place where the formed bruise, if it is a single local area or scuff the entire surface, if smudge a lot. If this tree, better suited to the skin, if metal drip any solvent and gently RUB on the affected place.
Cover the area with a new layer of paint. It is best to hold the painting in two stages. The first time add a thin top layer, and then apply the already more dense, but not overdo it, to not have outstanding plots.
Varnish surface for maximum alignment tone and thickness of paint. Polish will smooth out the last bumps and streaks will be over. Gently wipe the item from dust and dirt and install it back. That's all.